Xp usb troubleshooting

http://support.microsoft.com/kb/310575

hardware problems such as high or low power

If no devices work when you plug the devices into the root hub, verify that the power requirements of the bus are not being exceeded. USB devices can draw a maximum of 500 milliamps for each connection. If a device tries to draw more power than this, the specification recommends that the computer should be able to disable that specific port until the computer power is cycled (this is known as "suspending" the port). In addition, if the device draws less than 50 milliamps, the port never becomes active.