2002 Renault Scenic starting problems

I had problems starting my car, and a freind of mine fixed it for me (not sure what he did) the car started fine and then my gearbox whent. I had the costly problem of having to recondition the gearbox, but ever since my car was returned from the garage to me, the car would not start properly, since then i have had 2 seperate garages look at the car, and they have changed the fuel injector, replaced the glow plugs, tested the ECU chip on the car (came back with no problems) and had the car totally looked over and the car will not start and both garages give up and no longer know what to try. any suggestions would be greatly apreciated. thank you