I have a Dell Optiplex 330 and have recently done a Windows XP repair. After it was finished I was able to use the computer just fine. Now I take it back to it's original location and plug in the OEM mouse and keyboard and they both work until Windows XP loads. As soon as windows loads the lights go out on both the keyboard and mouse.
I ended up having to reload XP. Is what happened is that when I ran the repair it hung up and I had to power off so I think something got corrupted in the OS. I did a full reinstall and now it works fine.