CPU fan starts then stops.

[DoomedSoldier]

Computer specs:
Core: i7 7700K
Videocard: 1060 6gb Gigabyte
Motherboard: Asus H110M-K
PSU: Corsair RM850X

Yesterday, my little brother ran into a problem with his computer. We wanted to upgrade it from an i5 to an i7.
The motherboard is brand-new as well.
We unplugged everything except the CPU fan and the only think that happens is that the fan spins for a few seconds and then stops.

We tried bread-boarding, we tried a different PSU. We even tried it in a different motherboard and it worked fine on that motherboard.

 

[Gingerbread]

Does the CPU overheat? Have you tried a CPU stress software and see whether the CPU fan starts working once the CPU temps go up?

 

[tsnor]

Computer specs:
Core: i7 7700K
Videocard: 1060 6gb Gigabyte
Motherboard: Asus H110M-K
PSU: Corsair RM850X

Yesterday, my little brother ran into a problem with his computer. We wanted to upgrade it from an i5 to an i7.
The motherboard is brand-new as well.
We unplugged everything except the CPU fan and the only think that happens is that the fan spins for a few seconds and then stops.

We tried bread-boarding, we tried a different PSU. We even tried it in a different motherboard and it worked fine on that motherboard.

"...We even tried it in a different motherboard and it worked fine on that motherboard..." That would make me suspect the MB. Is it still in warranty ? MBs do crack when you push parts onto them like pushing down to seat a HSF. They also get bent pins in the CPU socket when you install a CPU slightly wrong.

Can you describe what you did when you breadboarded, and exactly what you saw ? "..We tried bread-boarding,.."

Its long, and most of the material does not apply but please read this because it is full of things you should check: http://www.tomshardware.com/forum/261145-31-perform-steps-posting-post-boot-video-problems