Someone turned it off!.
That's my initial thought,but I'd also suggest fully testing the system,full,part sets etc.
When was the system last serviced ?,and maybe you should also invest in a new battery,(as a precaution),they should be changed out at 3 to 5 yrs max.
If you decide to change the battery then ALWAYS isolate mains power BEFORE you open up the control panel.
Be safe :)
e manno, September 2013