That sounds like what happened to me this summer. I had to pull the fuse, and then I called Circuit City and they said to bring it in. They reconnected the fuse, the alarm went off, and he hit the button and it stopped. What the heck? I did that at home multiple times and it didn't work! I felt a little stupid, but I guess whatever works. Anyway, yeah, take it to the installer and see what they say. Maybe it'll fix itself while you're there just like mine did.
So did I. It sucked having to actually use a key.