To reset the cash register, turn the plug off at the wall, then hold keys 3, 8 & 13 (Not on the number pad on the right, but all the way to the left, 3rd key from the top and the 2 buttons next to it).
WHILE holding those numbers switch the plug back on. The register should now be reset.
Hop this helps!
Francois Roux, April 2011