If all else fails, try this link :http://searchwin2000.techtarget.com/tip/1,289483,sid1_gci996522,00.html
The title of the topic reads 'Lack of response after USB-PS/2 keyboard switch'.
It mentions adjusting some registry settings which are apparently overridden when a USB keyboard is plugged in a machine that normally hosts a PS/2. Again, i'm not sure if this is anywhere near the solution, but problem solving is a process of elimination and not an 'i'm right and your wrong' ego trip !!
PS. here is a direct quote from the article :
'Note that a PS/2 keyboard will still allow access to BIOS and will work in the boot-loader; it just won't work correctly in Windows. (It will, however, usually work in the Recovery Console.)'
Uh, d00d, he can to get into BIOS !!!