TEC MA-1450-1 Series Shutoff?

Periodically the register will shutoff during a transaction. The amount is entered into the dept key and validated, then the machine shuts off. We turn the machine back on and the display is 0.00 and we cannot push any buttons to make it work. We unplug and replug the power cord and log back on and then we can operate the machine again; this has a 50% success rate. This has been happening for about a week sometimes several times a day. Any suggestions?

Lisa
March 2012