Citroen C3 immobiliser / wont start

Hi, I started having intermitent problems with the car deciding not to start, then starting after I had reset the key. It would happen randomly once or twice a week then one day it just wouls not respond. When you turn the key all the lights on the dash light up, brightly but nothing at all. Ive had the keyu checked and it looks ok and the central locking all still works. The garage have told me to take it to a Citroen garage which I cannot afford at the mo. Any Ideas??