How to fix veritas 8c alarm?

Recently moved into a new house, the previous owners left instructions for operating the alarm and the instruction booklet it worked perfectly until a power cut, then when it came back on the power light was flashing and on trying to set the alarm all I got was 10 beeps. I hadn't time to mess with it so I left it, went to it this morning and zilch,nothing no power at all, changed the main fuse on the wall switch still nada! Took the front cover off and the post it note on the battery said renewed in July 2013, please any ideas?

Brian Atkinson
June 2017