How can I get my alarm to stop going off every time I plug up my pc1555mx ?

My power went out the other day and when it came back on, my alarm was going off and it won't stop. I unplug it, then plug it back up & the siren keeps going off. It shows that it is armed, but it isn't. I had to unplug it until I can get it fix. I have a pc1555mx ranger american system.