my strobe light is flashing and i can't turn it off!?

I have an Accenta 8 mini alarm system(nearly 10 years old). I have not used it for over 5 years. After turning my elec off to do a job, when i turned the power back on the strobe light on the alarm box(on the front of my house) was flashing. Even when i turn the power off now, the light still flashes??? What do i need to do?? Please help.