USB device detection in Winxp

Hi,

I have a 500MB u***** flash drive. When I plug it into my WinXP (SP2) desktop computer, the system couldn't detect it. If I plug it in before the system is powered up, then my computer will detect it and I could use it.

I tried this flash drive on my laptop (WinXP SP2) as well. It's plug&play.

I couldn't figure out what went wrong with my desktop. Does anybody have any idea? I would appreciate if anybody could help me out on this.

Thanks.