Whats wrong with my immobiliser on my ford fiesta 1.1 lx?

I cant seem to start my car!!! its the 1995 ford fiesta 1.1lx and the PATS light comes on the for the normal 3-4 seconds and goes out with no faulty code flashing at me however the engine doesnt crank when i turn the key and the electrics on the radio drop out until i return the key to position II can anyone help before i get ford to take it away to be looked at
thanks (newventures@hotmail.co.uk)