Keyboard locks up after keying NUM-LOCK or CAPS-LOCK
Some early AMI BIOS ROM's have a timing problem in the
keyboard controller. Boot the system and read the BIOS serial
number: if it ends with KA,KB,KC,KD,KE or KF, this is one of the
bad chips. Even though AMI has not made these chips since 1986,
some computer manufacturers still have them in stock. The only
solution is to replace the keyboard controller chip.