2004 Volkswagen Other Cold start problem

My vw touran will not start in cold weather, I have a new battery, new starter motor, glow plugs and glow plug relay changed but this morning when temp was 5c the car took 10 mins to start. I turn the key and wait for the glow plug light to turn off and then try to start it up my the engine just turns over without firing up, the glow plug light flicks on and off while I'm trying to start up engine. I keep trying this until eventually the car fires up once that happens it then cuts out and I try again until the engine just runs normally!