It sounds like you aren't logged on. Try pressing 1 then LOG. If it errors as soon as you press the numeric buttons, then you probably have lost everything from the machine in which case, a dealer will need to RAm clear it, replace the battery and setup the system areas ready for you to re-program it. this is common if the machine has been unplugged for a while.
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If anyone is looking for a TEC MA1450 operating manual, try here
http://the-checkout-tech.com/manuals2/cashregisters/tec1.php
Mark, February 2010