Veritas 8C?

Hi, We've had a veritas 8C alarm set up in our house for the last few years (it has been installed when the previous owners were living here). It's given us no problems as we were given the code and instruction manual.

Today though the alam has just stopped. There's still power, but the unset light is constantly on. The Power led (green light) constantly flashes and entering our code does nothing.

Is there anything I can do to reset the system?