My Volkswagen Golf GTI 1.8L Turbo 4 CYLINDERS won't start/ It starts perfectly sometimes and on some days too I spend over 30 minutes trying to start it. I hear the engine cranking like its gonna start whenever I turn the key but it doesn't start. I have changed my spark plugs, coils. So what could be the possible cause of this problem. Could it be my fuel pump or just a different problem?