how can i reset my optima 6 zone alarm?

had this alarm over 10 years never had a problem untill we had an area powercut last night and when the power came back on so did the alarm . we put our code no in and pressed reset but it just kept going . so had to turn electic off again to silence it . checked all three fuses they seemed ok but renewed them anyway (no joy) but noticed battery appeared to have been leaking . so we went to maplinns they tested it and said the charge was down and we needed a new one £27 . we got it put everything together and put code in pressed reset and it still didnt stop alarm going off . anyone got any ideas how to resolve my problem please!!!!!!!!!!!!!!