remote central locking?

my husband has a renault laguna sport 1.8 16v 1999.

my son owned the vechicle before us.since we have had the car the central locking will not work. we have tried everything that we have been told to do, but it is still not working. the key fobs have had new batteries, and have been synchronized with the receiver unit. my husband has had the receiver unit out and put the hair dryer on it incase it was damp, but nothing. the car was standing in the snow for three weeks or so. please does anyone have any idea what the problem could be.