9800 with 9827 - Resetting problems!!?

I have purchased a second hand 9800 scantronic system with 9827 keypad, however it came without codes. I have the manual, which I have followed for a '1st stage reset' (pin method with battery), but this isnt having the desired effect.
The display is blank, only the ac LED illuminates, with the day LED illuminating red upon keypad codes being entered. The keypad alarm tone is on constantly when powered up.
Could it be a faulty battery not giving enough voltage for kick start? or is there something else I should be doing?
Any help or suggestions gratefully appreciated