Originally Posted by Schoenfeld
Before changes to the licensing can be made, the "unprotect" jumper must be set. While a license code is being checked for validity, the whole computer freezes (mouse pointer does not move) for a few seconds. You only get this far if the "unlock" jumper is set, so you're safe when the jumper is open.
D'oh! Hadn't thought of that
Pretty obvious in retrospect