My Accenta alarm is flashing and I cannot make it stop?

I have an Accenta Alarm which I have never used since I bought the house 4+1/2 years back. (I don't know the model)
The Alarm is flashing on the front of the house. The alarm panel has "no" tamper light on or flashing. Only the number buttons are alight.
The panel is not reacting when I press any of the buttons. I know the security code but it does not work
What can I do to stop the alarm flashing?