Have the above system. Was working perfectly. Had the mains switched off to do a shower repair. When I switched the mains back on the alarm would not reset. No red light showing in the top left corner of the keypad where it normally shows. When I press any number on keypad the numbers all light up ok. Tried the resetting procedure but still no red light. All the sensors red lights working ok.
Some corroberative evidence to suggest that methyl speaks the truth.
http://www.diynot.com...iewtopic.php?t=276781
You will have flattened a battery (if it was on its way out) whilst the mains was switched off.
Replacing a battery back-up should be a DIY job - try Maplin for the replacement - unless your system is under a maintenance contract (in which case you will have to pay through the nose to get the maintrenance company to come out).