How to troubleshoot USB device problems that may occur after a portable computer that is running Windows Vista resumes from sleep or from hibernation

This article describes how to troubleshoot problems that may occur in USB devices after a portable computer that is running Windows Vista resumes from sleep or from hibernation.

Problems that can occur

When a Windows Vista-based portable computer resumes from sleep or from hibernation, the following USB device problems may occur:

• You may receive an error message.
• The USB device may not work.
• The USB device may not work as expected.

How to troubleshoot the problem

To troubleshoot this problem, try one or more of the following methods:

• Unplug the USB device, wait about five seconds, and then plug the device back in. If you are using a hub, unplug the hub, wait about five seconds, and then plug the hub back in.
• If you are using a USB hub, try to use the device without the hub. If you verify that the hub is the issue, use one of the following methods, depending on your scenario:
  • If the external power supply for the hub is not connected correctly, connect the external power supply correctly.
  • If there are too many devices plugged into the hub, unplug some devices.
  • If the hub does not function correctly, you may have to replace the hub.
• If your USB device is connected to a USB port on a portable computer docking station, try to connect the device directly to the USB port on the portable computer. If you verify that the problem is caused by the docking station, and the steps in this article do not resolve the problem, contact the manufacturer of the docking station for additional assistance. For information about how to contact the manufacturer of the docking station, visit the following Microsoft Web site:
  http://support.microsoft.com/gp/vendors (http://support.microsoft.com/gp/vendors)
  
  Microsoft provides third-party contact information to help you find technical support. This contact information may change without notice. Microsoft does not guarantee the accuracy of this third-party contact information.
• If the USB device is powered from an external source, make sure that the power from the external source is available to the device when the computer resumes.
• When you use USB 1.0 devices on a USB 2.0 capable system, the device may not function correctly or may have performance issues. To resolve these issues, you may have to replace the USB device with a USB 2.0 capable device.
• Install the latest updates for Windows and install the latest drivers for the USB device.
  
  To install the latest updates and drivers, visit the Microsoft Windows Update Web site.
  http://windowsupdate.microsoft.com (http://windowsupdate.microsoft.com)
  If there are no updates available for the USB device on Windows Update, you may have to contact the hardware manufacturer for information about updates.
  For information about how to contact a vendor, visit the following Microsoft Web site:
  http://support.microsoft.com/gp/vendors (http://support.microsoft.com/gp/vendors)

More technical information for advanced users

This section describes additional technical information about why this problem occurs and how you can change a value in the registry if other methods do not resolve the problem.

How the problem is indicated in Device Manager

Sometimes, Device Manager does not indicate that the USB device is not working. Or, Device Manager indicates that there is a problem by displaying a yellow exclamation mark next to the entry for the device.
For more information, click the following article number to view the article in the Microsoft Knowledge Base:

Why this problem occurs

This problem occurs because the Plug and Play operation that is performed when the computer resumes from sleep or hibernation does not correctly recognize the USB devices. When the computer is connected to many USB devices and resumes from sleep or from hibernation, multiple and concurrent Plug and Play processes are required. In this scenario, sometimes the Plug and Play operation cannot recognize all the USB devices that are connected to the Windows Vista-based portable computer. Therefore, the USB devices may not function correctly.

A Plug and Play operation may also not correctly recognize a USB device for the following reasons:

• An external power failure occurs on the powered hub or on the device when the computer is in hibernation.
• A device is unplugged during hibernation.
• A device is plugged in during hibernation.
• A device driver is out of date, corrupted, or incompatible.
• A device does not fully support hibernation or sleep power states.

Advanced troubleshooting steps

If other methods do not resolve the problem, you can change the value for the AdditionalCriticalWorkerThreads registry entry. To do this, follow these steps.
Important This section, method, or task contains steps that tell you how to modify the registry. However, serious problems might occur if you modify the registry incorrectly. Therefore, make sure that you follow these steps carefully. For added protection, back up the registry before you modify it. Then, you can restore the registry if a problem occurs. For more information about how to back up and restore the registry, click the following article number to view the article in the Microsoft Knowledge Base:

1. Click Start
   Collapse this imageExpand this image

   
   , type regedit in the Start Search box, and then click regedit in the Programs list.
   
   
   Collapse this imageExpand this image

   
   If you are prompted for an administrator password or confirmation, type your password or click Continue.
2. Locate and then click the following registry subkey:
   HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Executive
3. In the details pane, right-click AdditionalCriticalWorkerThreads, and then click Modify.
4. In the Value data box, type 2, and then click OK
   
   Note You can specify a value that is between 1 and 16.
5. Exit Registry Editor.

Similar problems and solutions

For more information about similar problems and solutions, click the following article number to view the article in the Microsoft Knowledge Base:

For more information about similar problems that may occur when a Windows Vista-based computer resumes from the sleep or hibernation power state, click the following article numbers to view the articles in the Microsoft Knowledge Base: Microsoft provides third-party contact information to help you find technical support. This contact information may change without notice. Microsoft does not guarantee the accuracy of this third-party contact information.