Scantronic 9448 Faulty following severe HV voltage drop?

My Scantronic 9448 Control Panel (Approx 15 yrs old), no previous problems, developed a fault during a voltage drop from 230v to 80v for 12hrs, during gale force winds. During this time it screeched and buzzed until I disconnected it from the mains. When the system voltage recovered to 230v I reconnected it. The green power light came on but nothing else. When I tried to enter the user code, the internal alarm and then the external alarm operated for 20 mins. I could not stop it even, by disconnecting the mains supply. Can it be reprogrammed, if so how? Is there an anti-tamper devise on the control box? Will the alarms operate and can I stop them? Any help please?