Brand new PSU with very weird issue

[Ortegal]

I just finished a brand new build with a corsair RM650x modular PSU. I plugged all the cables correctly but, at first, the PC wouldn't turn on. The power LED on the motherboard would turn on, but nothing happened when I pressed the power button.

After unplugging and plugging all the modular cables again, the PC turned on and I was even able to install Windows, but when I turned it off, it wouldn't turn on again!

Eventually, I realised that every time I turned the PC off, it would only turn on again if I
switched the places where the modular cables attach to the PSU and turned the switch on the back of the PSU off and on again. After dozens of tries and combinations, I haven't been able to simply turn off the PC and turn it back on without doing that.

Any idea what might be causing this?

Build:
Corsair Spec-Alpha case
Core i5 6600k
Cooler Master Hyper 212x
Asus Z170 Mark 1
Samsung 850 Evo 250GB SSD
WD Caviar Blue 1TB HD
Gigabyte GTX 1070 G1 Gaming
4x4GB DDR4 2133MHz Kingston HyperX Fury

 

[brispuss]

Possibly a marginal electrical connection that may not be making proper contact on or within the PSU.

For the cables from the PSU, check that the pins and/or ferrules within the cable connectors are not damaged, bent or otherwise out of shape. This applies especially to the ferrules, as they are prone to being squashed etc.

If no success, then try the RM650x in another computer, and/or try another known working PSU.

 

[Ortegal]

Possibly a marginal electrical connection that may not be making proper contact on or within the PSU.

For the cables from the PSU, check that the pins and/or ferrules within the cable connectors are not damaged, bent or otherwise out of shape. This applies especially to the ferrules, as they are prone to being squashed etc.

If no success, then try the RM650x in another computer, and/or try another known working PSU.

The RM650x is the only PSU I have on me right now, but unless I can solve this I will have to try to find another one to test this.

I just checked the pins and didn't find any out of the ordinary. And the issue just got wierder. I just found out that if I press the power button right after turning the PSU switch on, the PC turns on without me having to switch the modular cables. At least it got simpler to power it on now, but I still welcome any suggestions to solve this.

 

[brispuss]

This is more suggestive of a faulty PSU.

As mentioned previously, try the RM650x in another computer, and/or try another known working PSU (borrow computer/PSU from friend, neighbor etc if necessary).