Thanks for the responses so far: I have tried all the verifications suggested (swapping, swapping other h/w in, to other machines, one out, etc.) and there is no difference. I am reasonably confident that it's not the h/w, since they operate during power up and on other bits of kit. Although there's USB devices plugged in, the kb/mouse are definitely PS/2 style and are in the right connectors. So I am pretty stumped.

I also tried to boot from the install CD and it loads all the mini ports and then....

.. hangs waiting for something, so I can't even do much to attempt to repair a damaged installation, which is less than good.

Any other ideas?