If you can't even do a half clear, then I'd say you have a bad memory battery (should be replaced every three years). This means all programming will be lost. Might pay to get a dealer to check it out.
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If anyone needs Samsung / Sam4s SPS-1000 manuals, try here:
http://the-checkout-tech.com/manuals/cashregisters/Samsung2.php
Registerman, December 2010