deepstrike

I have been happily using two external hard drives and my psp in connection with my computer for a number of months now until a couple of days ago when they all became unknown devices not recognised by my computer. i share my computer with other people but i've been assured they havent changed anything so why the sudden error? if i disable usb 2.0 in the bios the computer does detect them but they run very slowly. although this helps as a temporary measure i'd like to find out how to get them running at full speed again. My usb cables all work fine, and the devices work fine on other computers. any help would be appreciated, thanks