central locking fault ford fiesta?

I own a for fiesta flight 1.3 97 plate
returning to the car after doing some shopping i turned the key in the drivers side and nothing happened i went round to the passenger side and tried the system unlocked then locked itself again i managed to get the door open by turning key and openeing dor quick with the passenger door open the locking system will continuosly lock and unlock untill the passenger door is shut then it will lock if i leave car for an hour or so trying the drivers door works once but tries after this will make the same problem above occur i phoned up a ford dealer and they quoted me £81 an hour for a diagnostics check and said that depending on the fault it could be a £500 repair bill which seems a bit much

Duane
December 2007