When you plug a USB device into a Windows XP-based computer immediately after the computer comes out of standby (S3) or hibernate (S4), the computer may not recognize the USB device. When this issue occurs, the USB device may be listed in Device Manager as an unknown device, and you may receive the following warning message:

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This issue occurs because, when the computer comes out of S3 or S4, there is a five- to ten-second period when the selective suspend feature of the USB driver will interfere with detection of a new USB device connection. The time period depends on several factors. This includes the following factors:

•	Host controller hardware
•	Attached hubs
•	Attached devices
•	USB driver versions
•	Support for USB 2.0
•	Additional system hardware or configurations that may change the timing Note There may be other reasons that a USB device is not detected. For a related Microsoft Knowledge Base article, see the "SIMILAR PROBLEMS AND SOLUTIONS" section.

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To work around this issue, use one of the following methods:

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Method 1

After the computer comes out of S3 or S4, wait five to ten seconds before you plug the USB device into the computer or hub.

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Method 2

After the computer comes out of S3 or S4, unplug the USB device, and then plug the device back into the computer or hub.

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Method 3

Use the Device Manager to scan for new hardware. Follow these steps:

1.	Click Start, click Run, type Devmgmt.msc, and then click OK..
2.	On the Action menu, click Scan for hardware changes. This causes Windows to recognize new devices.
3.	Close Device Manager and Control Panel.

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Method 4

Disable power management of the USB hub.

Note If you perform the following procedure, you may also reduce the battery life on a portable computer.

To disable power management on the USB hub, follow these steps:

1.	Click Start, click Run, type devmgmt.msc, and then click OK.
2.	Expand the Universal Serial Bus controllers node, and then follow these steps for each USB Root Hub that is listed: a. Right-click the USB Root Hub, and then click Properties. b. Click the Power Management tab. c. Click to clear the Allow the computer to turn off this device to save power check box, and then click OK.

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Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.

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For more information about advanced troubleshooting tips for general USB problems, click the following article number to view the article in the Microsoft Knowledge Base: For more information about how to troubleshoot unknown devices in Windows XP, click the following article number to view the article in the Microsoft Knowledge Base:

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