CPU fan stops after POST and system shutdown

[IrOnGiMp]

I have acquired a Alienware Area-51 M15X R1 for free as the owner didnt want it. The problem that I found is that upon startup, the CPU fan spins up fine, but after POST it stops. I replaced the motherboard today, and applied new thermal paste where needed. Although I believe the problem to be the fan not working properly to cool the system, I need other thoughts, as in, to get the fan to spin as it should. Thanks!!

 

[lesterlol69]

could be a faulty fan or loose/broken fan wiring

 

[IrOnGiMp]

could be a faulty fan or loose/broken fan wiring

Thanks for a response. While I do not think that the case, because I swapped both fans to the other's location. Both fans ran properly. Only the CPU fan, while plugged into its proper place, performs the way I described in my question. But for the sake of ruling out a bad connection to the fan, I have ordered a certified replacement, and will update whenever it comes in.