I work from two pc's - one at the office (both xp pro), and one at home. So that I always have the same files with me all the time, I work directly from a portable hard disk. I know that this probably isn't the best idea in the world, but it's worked perfectly for almost a year.
At the office, it still works fine, but at home, the usb drive keeps disconnecting, and I have to re-boot every time it happens, and I have lost work through it several times. It's only started doing this recently, and it's a real pain!
The only thing I can think that I've changed, is that I've changed my anti-virus from Bullguard to AVG (free edition). Could that be the cause?
Check in Control Panel>System>Hardware>Device Manager> scroll to and open USB Controllers, right click each listed USB Hub and select properties then select Power Management, make sure there is NO tick in the box for `allow the computer to turn this device off to save power`, if there is a tick, remove it.