Wow, I've never heard of this happening before. Hmmm, have you tried using the PS/2 connector with the keyboard? If so, does that eliminate the problem? Try using different USB ports to see how it reacts. Reboot. I'm sure you have SP1 for USB 2.0 support. If so, how about your hardware? Are your keyboards compliant with USB 2.0 too? I highly doubt this will have anything to do with your problem though, but just a thought. Are you using wireless keyboard? I know the RF keyboards have the antennas going into the USB ports too with IR having line of sight.
Maybe the keyboard is dirty and sticking?
*Fact: Microsoft Window's Blue Screen of Death vs Computerforums.org's White Screen of Death. Which is worse?