Scantronic 9448 alarm?

Hi, just looking for some guidance please, a tenant has just moved out of a small flat i own, it has an old scantronic 9448 alarm installed, I've just discovered that the alarm has not been used since he moved in 5 years ago, it was working when he moved in. I've tried to get it working but to no avail. I've even reset the NVM, the panel does not respond to and key press, and the alarm sounds when power is applied, there are no lights showing except the green power key at all, the few times i've managed to get it silent, i've discovered its armed itself when it sounds i've got to remove power and disconnect the battery to stop it sounding. Do i need a new alarm panel or can anyone offer advice please.