USB/Mouse won’t move, can’t log into Windows

I’ve been working on a clients PC running Windows Media. Problems started when I couldn’t connect to the Internet. All was good in device mgr (no yellow !’s). Updated NIC driver, no change. Tried to use USB cable from PC to cable box, that wouldn’t work either. Called ISP and all was well on his end. Took PC home to run anti-virus, spam, malware. Booted up PC and now USB mouse/keyboard won’t move, so I can’t log into Windows (there is no PS/2 ports -small Dell box).

I set it up as a second drive in my PC, found a bunch of trojans and deleted them. Tried again in customers PC, still can’t move mouse/keyboard. Hooked up drive as second one again and ran chkdsk/r. Still not fixed!

Any ideas? Going crazy.