How can I fix my Scantronic alarm?

A few weeks back I went away for two days and when I returned I entered the house to find that the alarm did not register. When I looked at the main control panel the tamper light was flashing. I tried to reset it but it wouldn't...the tamper light remained flashing. I had been really windy so I checked the bell box was still secure - which it was. However, I then noticed that the LEDs in the bell box were not flashing, even though there should have been power to the box. I thought it may be the cable to the bell box which was faulty, so I took the bell box down and ran a new cable to it as a test - still no power. Thought it may be an electronic fault with the bell box - got a new one, but still no joy. I have tried resetting the whole system by cutting all power - nothing!!

Any help would be greatly appreciated as no-one seems to know what the problem is.