it needs a new battery, good battery, at good price Srcewfix Direct.
To put new battery in you MUST remove old battery first and turn off power to Alarm for 2mins, you MUST turn mains power first, leave mains on for 1min, put in new battery, put cover back on and try alarm.
If its still lockup repeat the above it till unlocked.
REPLASE BATTERY EVERY 3 YEARS.
Joe, Alarm Engineer.
November 2009