Volkswagen jetta 2004 not starting

Hi, so i own a VW jetta 2004 2.0 non turbo i had it for about a month then when the super cold temperatures hit i started to get starting problems at first we thought it was just natural cold, we used starting fluid and it started up days later happened and then started happening through the warm as well so my dad replaces the fuel filter fuel regulator, sparks plug wires, spark plug, cleaned air flow. And it won’t start without starting fluid … after it starts up and warms up you can start it without it but about id say 24 hours later it probably won’t start again without starter fluid, we thought it was maybe the fuel pump but it really doesn’t seem like it… but maybe it primes just fine and is 100% fine once it’s running no on road problems, it’s just that starting is the issue and we don’t know why. UPDATE Car would not start without starter fluid the 6 prime didn’t work, any other suggestions?

The next time you go to start the car after it has sat, turn ignition switch to run position so the dash lights come on for two seconds and then turn the ignition switch off.

Repeat this a half dozen times and then try starting the engine. If the engine starts right up, it points to a problem with the anti drain-back valve on the fuel pump assembly.