inermitten starting problems vw sharan 2.0 r reg help..!!!?

i can drive my sharan for a while but when i stop my car sometimes when i go back to start it it turns over but wont go, othertimes it will start after 5-10 attempts, sometimes it takes hrs, occasionally no prob at all. it also dies whilst driving and wont restart immediaely. there is no spark and the injection system fails (as discovered by the rac).
was told to replace coil pack ran fine for a few weeks now same problem yet again.