security code fiat punto 1997 diesel?

HI. My Fiat Punto R reg 1997 diesel doesn't start and has been diagnosed with a security key code problem. The glow plug light doesn't show and the security code key symbol stays on while the engine turns over but doesn't fire up. This happened just as I plugged my new Sat Nav into the previously unused cigarette socket for the first time. Is this just coincidence? I am told it will cost hundreds for Fiat to sort it without a RED key. I have only ever had a blue, and a blue with a red centre, as had the previous owner. A locksmith suggested removing the immobiliser, but my mechanic says that may not be possible on a diesel. This all seems ridiculous, as the car is not worth much, but has just got through an MOT and runs well. Any advice will be gratefully accepted.