resetting nvm on a accentra 6?

hi can anyone tell me how to reset the nvm on a accentra 6 system. i had a power cut resulting in a loss of power to the keypad, whenever i try to put power back alarm sounds and i cannot use keypad. i do not have codes, so need to reset nvm to factory setting of 0123.

thank you in advance

Gary Varley
August 2010