Intermittant keyboard failure

My keyboard quit working a couple of days ago. I went ahead and plugged in a new keyboard and for two days the computer worked fine. However, this evening the new keyboard quit working as well..

I tried both the new keyboard and the old keyboard on another machine and both worked. Apparently the problem isn’t my keyboard.

Any idea what might be causing the problem or what components I could run a diagnostic test on?
I have an ASUS CUSL2-C motherboard and I am running Windows 2000 Pro.