What sort of keyboard do you have? Is it USB or a PS/2 connector on the cord.

If it's USB, then try using a PS/2 keyboard instead. If it's PS/2, then the socket may be 'blown' if the keyboard cord has been dislodged at some stage with the sytem powered up.

Knowing the make and model number of your PC or of your motherboard would help here. (This is a hardware issue, by the sound of things) Specific details about your system's hardware will help us to give good advice, as BIOS options differ from system to system.