If when it activates, and you input your code and it will not silent - it could be that it has locked up and defaulted back to 0123 as a user code. My advise would be to completely power down - power up mains first enter your code or the default code. Also these panels lock out in tamper - so if a tamper circuit is open you will not be able to user your code as it will lock you out. Tell me more sysmptoms - when was it installed and how long has the battery been in ?
Mark, May 2011