When you plug an external USB hub into your Windows XP computer, and then unplug the USB hub, your computer may not be able to enter the low-power idle state (C3).
To determine if your computer is effected:
1. Add the %C3 Time or C3 Transitions/sec counter into Performance Monitor.
2. Plug in an external USB hub.
3. Unplug the external USB hub.
4. If the %C3 Time or C3 Transitions/sec counter remains stuck at zero (0), you have this problem.
NOTE: This problem is the result of the USB hub entering a race condition that prevents your computer from entering the C3 state. There is currently no fix, but hopefully the next service pack will address this issue.