This is not an ususual error with Compaqs and is a result of a damaged PS/2 keyboard port. I would first check your keyboard pins to be sure they are all present and accounted for. Make sure they were not bent or one pin broken. If it is possible that one may be missing, you should replace the keyboard.

However, it is most likely that the port itself has failed. In this instance, your only option is to purchase a USB keyboard.