Does it stop when you press clear? If not, I'd try an initial clear. Run through the procedure for the initial clear in your manual. Make sure you do not do the Memory all Clear. That will lose data, but the initial clear just stops the current task.
If you need a manual, C-tech has it here:
http://the-checkout-tech.com/manuals/cashregisters/Samsung2.php
Registerman, April 2011
