problem with scantronic 9448?

hi guys
installed this panel approx 15 yrs ago replaced a pir 10 yrs ago as it had gone dead.recently another pir seemed to have gone same way so went to replace it.opened cover int. sounder starts enter key code ok.removed 24 hr and n/c wires.paying attention not to cause any shorts removed neg wire which caused the panel to have a nervous breakdown all leds flashing int sounder going berserk ext sounder activated no bleep when pressing keys, removed mains fuse stopped everything, all fuses ok.i was surprised when bell stopped with mains fuse removed and battery disconected
Do you think the panel is now us or do you think i may be able to reboot to default, why would removing power from 1 pir cause all this