'96 406 Immobiliser issues?

Hi there

I've got a '96 Peugeot 406 1.9TD with a 4 digit immobiliser keypad which has developed a fault.

Before putting the key in the ignition the red light is flashing as normal to indicate that the immobiliser is active but when you turn the key to position two the red light continues to flash but is barely visible (like the power is being drained from it). The keypad will not accept any codes and makes no audible noises when any key is depressed. I have tried getting additional power from another car but that made no difference.

I've checked the wiring at the back of the keypad and it's all intact and correctly connected - anyone have any ideas what's going on?

This happened without any previous issues from the system - I'd parked the car up in Tesco, went for some shopping and when I came back to the car - nothing!

Any help would be greatly appreciated