No mains power light to my keypad?

i have a scantronic 9800 Micro processor intruder alarm originbal fault was faulty battery back up so i changed this now i have no mains power to my keypad, the keypad keys make the blip noise when pressed and the 2 small screen light illuminate but there is nothing on the small screen display and the mains green light is not illuminated, the display did show rP fault which is the remote keypad missing faulty prior to battery going completly dead any ideas??, thank you.