How to troubleshoot unknown devices that are listed in Device Manager in Windows XP

Device Manager displays a list of all devices that are installed on a Windows XP-based computer. When you view device information in Device Manager, you may see a device listed as Unknown Device next to a yellow question mark. It may be difficult to determine the cause of this unknown device, because there are few indications of what generates it. This article discusses the possible reasons that an unknown device may appear in Device Manager.

The main reason for Unknown Device to display in your Device Manager is because you have a device that is not working correctly. To fix this issue, obtain an updated driver for the device.

Use the following methods to enable Windows to recognize your device.

Method 1: Windows Update

Visit the following Microsoft Web site to see whether the Web site autodetects an updated driver for your device. Install all recommended drivers.

Method 2: Download and install the latest driver from the Internet

When you download a driver from the Internet, download the Windows XP version of the driver when multiple Windows versions are listed. Use one of the following options:

• Visit the Web site of the computer manufacturer if the device came with the computer.
• Visit the Web site of the device manufacturer if the device was installed after you purchased your computer.
• Visit the Web site of the device manufacturer if the device was preinstalled on your computer and the computer manufacturer does not have an updated driver.

Look for a Drivers section or a Download section on the manufacturer’s Web site, and search for the device name. Download and install the Windows XP version of the driver.

Advanced user section

This section is intended for advanced computer users. If you are not comfortable with advanced troubleshooting, you might want to ask someone for help or contact support. For information about how to do this, visit the following Microsoft Web site:

Causes of unknown devices in Device Manager

• The device does not have a device driver: When a device driver for a device is not available, Device Manager displays the device as Unknown Device and puts it in the Other devices branch. This is very common with universal serial bus (USB) and Institute of Electrical and Electronics Engineering (IEEE) 1394 composite devices. Also, a status of Error Code 1 or Error Code 10 may be displayed when you view the properties of the device in Device Manager.
  
  Note Most USB and IEEE 1394 devices function correctly without additional device drivers because they are configured by the drivers that are included with Windows for these bus types. However, an additional device driver is needed if the device does not fit the defined and supplied Windows class drivers. If the bus cannot identify the device, it interprets the device as a composite device and then reports it as such in Device Manager.
• You are using a Microsoft Windows 98 or Microsoft Windows 95 Device Driver: You cannot use virtual device driver (.vxd) files that are common to Windows 98 or to Windows 95 drivers in Windows XP. If you try to install them on your Windows XP-based computer, the device may be listed as unknown in Device Manager. This typically occurs when the device driver manufacturer does not correctly differentiate between the two drivers or assumes that Windows XP can use Windows 98 or Windows 95 .vxd files.
• Unrecognized Device ID: Every hardware device has a special identifier that is used by Plug and Play. This identifier can include several different types, such as vendor ID, device ID, subsystem ID, subsystem vendor ID, or revision ID. If a device ID is not present, or your Windows XP-based computer does not recognize the device ID, Device Manager may list the device as unknown.
  
  Note Software programs that require virtual hooks into hardware may create these devices. Additionally, devices that bridge between bus types, such as a device driver that enables a parallel port device to emulate a SCSI or an AT Attachment Packet Interface (ATAPI) bus, are also known to generate an unknown-device response in Device Manager.
• Faulty Hardware or Firmware: Faulty hardware or firmware may cause a device to be displayed as Unknown Device in Device Manager. Software-only device drivers do not expose a device ID, and there is no standard method for installing these devices. Some manufacturers install the device by using the InstallShield installation program or a similar method. Be aware that software installed by other methods may not be completely removed when the device is removed in Device Manager. Therefore, you may have to check the registry to verify that all entries are removed.

Troubleshooting for advanced users

Troubleshooting software issues

Use any of the following methods to determine whether an unknown device is being created by software:

• Start your computer in safe mode
  
  Although not 100-percent reliable, starting your computer in safe mode can be one of the easiest ways to determine whether the unknown device is created by software.
  
  To start your computer in safe mode, press F8 after you restart your computer. On the Windows Advanced Option Menu that appears, use the ARROW keys to select Safe Mode, and then press ENTER. If the unknown device is no longer listed in Device Manager, it is likely that the unknown device is not hardware.
• Check the Startup folder
  
  If you suspect that a particular program is the cause of the unknown device, check the Startup folder on your computer to see which programs are configured to start when your computer starts. The Startup folder is in the following location on your hard disk, where C is the drive on which Windows is installed, and user profile is your user profile:
  C:\Documents and Settings\user profile\Start Menu\Programs
• Use the System Information tool
  
  The System Information tool can be useful when you have to determine the cause of an unknown device.
  
  To use the System Information tool to view a list of programs that start when your computer starts, follow these steps:
  1. Click Start, click Run, type msinfo32, and then click OK.
  2. Expand Software Environment, and then double-click Startup Programs.
     
     A list of the programs that are configured to start when your computer starts is displayed.
     
     Check the event log for errors that refer to any of these programs. If you find an event that is related to a program in this list, remove the program. Be aware that when a program creates an unknown device, it is not necessarily an indication that the program does not work, unless the program depends on that device to start.
  
  To use the System Information tool to view a list of problem devices, follow these steps:
  1. Click Start, click Run, type msinfo32, and then click OK.
  2. Expand Components, and then double-click Problem Devices.
     
     A list of the devices that are installed on your computer that may have a problem is displayed in the details pane, as follows:
     • The Device column lists the common name for the device, or the name of the device driver associated with it.
     • The PNP Device ID column lists device IDs, such as Peripheral Component Interconnect (PCI) ID, ISA ID, an ID for some other bus type, or an unknown type.
     • The Error Code column lists the error code associated with this specific problem. Frequently, the Device Manager error code helps determine what created the unknown device. For example, if your computer generates a "Bad or missing device driver" error message, three types of entries may be listed under Problem Devices, depending on the device type:
       • PCI PnP Device ID:
         
         Device Name | PCI\VEN_00000&DEV_0000&SUBSYS_00000000&REV_00\0&0000 | Error code
       • ISA PnP ID:
         
         Device Name | ?\PNP0000\0
       • Bad or Incompatible Device Driver:
         
         Device Name | ROOT\UNKNOWN\0000
• View the Setupapi.log file
  
  If the device has a meaningful name, use the information in the Setupapi.log file to determine the cause of an unknown device. By default, the Setupapi.log file is located in the %SystemRoot% folder.
  
  Sometimes the listed device name can be misleading. For example, a device may be listed as a serial device in Device Manager, when in reality it is not related to a serial port. This typically occurs when a partial Plug and Play ID is available, and Device Manager interprets it as a serial device. This interpretation may occur because of a compatible ID specified by the device. Again, this can be corrected by locating the startup program that may not be behaving correctly.
  
  Be aware that merely removing the unknown device in Device Manager does not work if a software program is the cause of the unknown device. You must remove the program and then restart your computer. If the unknown device is still listed in Device Manager after you restart your computer in safe mode, contact Microsoft Customer Support Services for help in removing the device.

Troubleshooting hardware issues

To determine the cause of an unknown device, use one of the following methods:

• Remove hardware devices from your computer
  
  Remove hardware devices one at a time until the unknown device is no longer listed in Device Manager. Be aware that this method may be time-consuming and is not always reliable.
• Determine whether the device driver is digitally signed
  
  When you install a device driver, and Windows detects that it is not digitally signed, you may receive a warning message and the option to cancel or continue the installation This message is displayed only if your computer is configured to display a warning message whenever an installation program tries to install a device driver without a digital signature.
  
  Note A device driver that is digitally signed can still be listed as an unknown device in Device Manager.
  
  For more information about driver signing for Windows, visit the following Microsoft Web site:
  http://www.microsoft.com/whdc/devtools/ddk/default.mspx (http://www.microsoft.com/whdc/devtools/ddk/default.mspx/)

You can block the installation of device drivers that do not contain a digital signature. Use this approach when you want to prevent any deliberate attempts to destabilize the computer. To do this, follow these steps:

1. Click Start, click Run, type control sysdm.cpl in the Open box, and then click OK.
2. Click the Hardware tab.
3. Under Drivers, click Driver Signing, and then click Block - Never install unsigned driver software.
4. Click OK two times.

To view a list of device drivers installed on your computer that are not digitally signed, use either of the following methods:

• View the Setupapi.log file
  
  Look for entries that resemble the following:
  The file (C:\Windows\inf\ntapm.inf) is not digitally signed, ignoring driver date.
  Installing section epatapi_inst from C:\documents and settings\user name\my documents\parallel port test drivers\epatapnt.inf
  An unsigned or incorrectly signed driver (C:\documents and settings\user name\my documents\parallel port test drivers\epatapnt.inf) was installed for Parallel ATAPI Adapter.. Error 0xe000022f: The third-party INF does not contain digital signature information.
  Copying file C:\documents and settings\user name\my documents\parallel port test drivers\epatapnt.mpd to C:\Windows\System32\DRIVERS\epatapnt.mpd.
  An unsigned or incorrectly signed driver (C:\documents and settings\user name\my documents\parallel port test drivers\epatapnt.mpd) was installed for Parallel ATAPI Adapter.. Error 0xe000022f: The third-party INF does not contain digital signature information.
• Use the File Signature Verification tool
  
  The File Signature Verification tool lists all the unsigned drivers that are installed on your computer. It creates a Sigverif.txt log that is located in the %SystemRoot% folder. Use any text editor (for example, Notepad) to view the file. To use the File Signature Verification tool to display a list of drivers that are not digitally signed, follow these steps:
  1. Click Start, click Run, type sigverif, and then click OK.
  2. Click Advanced, click the Search tab, and then click Look for other files that are not digitally signed.
  3. Click to select the Include subfolders check box, and then click Browse.
  4. Locate and select the %SystemRoot%\System32\Drivers folder, click OK two times, and then click Start.
  Review the list, and then contact the driver manufacturer for information about how to obtain an updated driver that is digitally signed.

USB devices that are based on earlier versions of the USB specification may create ghost devices that appear when the device is connected, and then disappear when the device is disconnected. Also, the device may work fine, but may create a disassociated unknown device. This is typically caused by firmware that is either outdated or configured incorrectly. In this case, contact the device manufacturer for updated firmware.

A ghosted device can appear if you manually install a driver for a Plug and Play device that the computer has already detected and installed. You can resolve this issue by deleting the ghosted device.

Similar problems and resolutions for advanced users

For more information about how to use Device Manager to manage devices in Windows XP, click the following article numbers to view the articles in the Microsoft Knowledge Base: For more information about the System Information tool, click the following article numbers to view the articles in the Microsoft Knowledge Base: For more information about how to troubleshoot with the Msconfig tool, click the following article numbers to view the articles in the Microsoft Knowledge Base: If the articles listed here do not help you resolve the problem or if you experience symptoms that differ from those that are described in this article, search the Microsoft Knowledge Base for more information. To search the Microsoft Knowledge Base, visit the following Microsoft Web site: Then, type the text of the error message that you receive, or type a description of the problem in the Search Support (KB) field.

The third-party products that this article discusses are manufactured by companies that are independent of Microsoft. Microsoft makes no warranty, implied or otherwise, about the performance or reliability of these products.