This is one of the odder issues I've come across to. I have Asus Eee 901 netbook running XP. The issue is with the USB ports: sometimes they appear to lose contact and this results into devices getting out of power for a moment. This isn't so big of an issue in itself, the devices can boot again just fine and most of the time I don't need to care about it, however my external HD just stops working at all. The device doesn't become available, it gets power but I guess Windows sends invalid command via USB and it doesn't get past initialization phase. This keeps happening no matter which port I change the device into so it must be a Windows, hardware or driver issue. The only way to fix it is to reboot Windows.

As of yet I haven't tried upgrading drivers, but I'm wondering if it is possible to reset USB as if the machine had rebooted without rebooting the computer?