Scantronic 9884+ will not set after a power cut?

Scantronic 9884+
During a recent power cut the user code reset back to the factory default. I changed it to our usual code and tried to set the alarm but it doesnt give me the usual exit tones. Normally when setting the alarm the exit tone sounds and then when I open the door to leave it changes to a continues tone for a few seconds until the alarm is set. However when I open the door to leave the tone does not change and after 30 seconds the tamper alarm sounds. Can anyone offer any help please?