One or more USB devices may not work after you start your Windows XP-based computer

When you start a Windows XP-based computer, one or more of the attached universal serial bus (USB) devices do not work. This article describes possible reasons why the devices do not work. Also, this article contains methods that you can use to make sure that your USB devices work correctly.

When you start a Windows XP-based computer that has one or more USB devices attached, or you plug a USB device into a powered USB hub, one or more of these devices may not work. These USB devices may be attached to a Windows XP Service Pack 2-based computer or to a Windows XP Tablet PC Edition 2005-based computer. You may not receive an error message in this scenario. Or, you may receive the following error message: Or, when you start your computer and connect additional USB devices to the computer until the total power consumption of the USB devices is more than the available power from the USB hub or port, one or more of the USB devices may stop working. Then, you receive the following error message: Similarly, if you then restart your computer with the same configuration, the same USB device or devices do not work, and you do not receive an error message.

Note These USB devices may be attached directly to USB ports on the computer or to an external USB bus-powered USB hub.

This issue may occur if one or more of the following conditions are true:

• You have too many USB devices attached to the USB hub. This issue occurs because the combined sum of the power requirements of the USB devices is more than the available power that is provided by the hub.
• You have a high-power USB device attached to a USB hub or to a USB port on the computer. For example, you have a USB hard disk, and the USB device exceeds the power limit of the hub or port. This issue typically occurs if the USB device can run with or without an AC power adapter.
• Your computer uses an internal hub. For example, a portable computer may have a single USB bus and may use an internal USB hub to provide two or more available USB ports on the computer. Suppose that you use the device without the AC power adapter. In this scenario, the available power from a single port may be less than expected if other USB devices are connected to the other USB ports on the same internal USB hub.

To resolve this issue, use one of the following methods, depending on your circumstances:

Method 1: Connect the AC power adapter to the USB device

You may have too many USB devices attached to the USB hub. The sum of the power requirements for the devices exceeds the power capacity of the hub. When you connect the AC power adapter to the USB device, the power requirement for the USB device from the USB port is greatly reduced.

Method 2: Connect the AC power adapter to the hub

You may have a high-power single USB device, such as a hard disk, that has the option of running with or without an AC power adapter. If you are not using the AC power adapter, the USB device may require more power than the power that is provided by the hub or by the port. When you connect the AC power adapter to the hub, more power is available.

Method 3: Replace a passive (unpowered) hub with an active (powered) hub

If you are using just one USB device, you might not need a power supply. However, if you are using several USB devices, the power requirements for the number of USB devices you are using may require a powered USB hub.

Method 4: Determine which USB device is not working or is causing the issue, and then connect the device directly to a USB port on the computer

To determine which device is causing the issue, follow these steps:

1. Disconnect all the devices from the USB hub.
2. Restart the computer.
3. Connect the devices one at a time until you receive the following error message:
   USB Power Exceeded
4. Try different combinations of connected devices to determine the most effective configuration.

For help with device problems in Windows Vista, visit the following Microsoft web page: