no response from keys?

Firstly, try jumping out of any loops:

Turn power off at wall
Wait approx 2 minutes
Turn key to PGM mode
Hold FEED button down while turning on at wall

Then turn key back to REG mode and try it
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If anyone needs more information, the Sharp XE-A202 manuals are here:

http://the-checkout-tech.com/manuals/cashregisters/Sharp11.php

Registerman
May 2011