P Reg A4 with starting/immobiliser problems, please help!

To all those who have come from my post in the newbee section, hello again. To all others, Hi, my name's Jason, I'm not a current Audi owner myself (a previous Audi GT owner though ) but a friend of mine is, she's a single mum and having a hell of a time with her car (not trying to play the sympathy card but just to give you an idea of how much she needs the car). Basically it's a problem to do with the immobiliser and/or the ecu I believe. History of the problem.... initially car was working fine then one day it just wouldn't unimmobilise, put the key in, turn it and the immobiliser light was just flashing, start it and within a second it would die. Eventually found a way around it, on the ecu, I think it's the ecu,(box in the back left corner of the engine bay?) there's loads of wires coming out, one in particular though, If you disconnect this wire, turn the key to the ignition position, re-connect the wire and start the engine it would run fine! Obviously you would have to do this everytime you turned off the engine. Now, last week it went in to have a couple of tyres changed and thats it, we went to pick it up and nothing, the immobiliser light flases no matter what you do to the ecu (if it is the ecu) the car just wont start, anyone got any suggestions, maybe it's a common problem? Your help will be so much appreciated, I said I'd do all I can to get her back on the road.

Many, many thanks