clio immobliser remote not working?

i have a 98 1.4 rt automatic and the central locking and immobliser have stoped working, 1st i had to press the key aginst the window to open it so i replaced the battery in the remote after that the red LED stop working on the fob but the remote seemed to work better now the it has stoped working completly, ive replaced the batterys in the fob agin but its still not working and the car wont start with out it, i dint know if its the fob or the reciever on the roof thats broke, any ideas on how to tell and how to fix this?