It may sound stupid, but have you checked your startup items? Even the really stupid stuff in the startup folder?! (Sometimes, the most obvious is the hardest to see.)
Barring that, I'd be looking at the device manager and all IRQ settings. You may have to drill down and see if things aren't trying to share the same DMA and address range too. However, you should be OK so long as other devices aren't trying to use the exact same settings. Otherwise, you may have to get into the BIOS to at least change IRQ's if there's a conflict.
These days, nearly everything plugs into a USB port including mice and keyboards. And that's fine for the average PC but not so good with a server that may need all available IRQ's for NIC's, printers, or something else. And since PS/2 keyboards pretty much have an exclusive IRQ1 set aside you might as well use it for a real PS/2 keyboard. And whatever IRQ your mouse may be using it may be better to change that too (the USB port, that is).
I can't say if that's the problem or not, but IRQ assignments are definitely worth checking.