New Motherboard RGB Lights Working, but Unable to Start PC

[Sturmgewehr_44]

I upgraded my system yesterday from a 4790k and Maximus VII Formula to an 8700k (and of course Dominator Platinum DDR4 @ 3200MHz).

Everything was normal afterwards. No problems whatsoever. I reused my AIO (Corsair H100i V2), temperatures were normal (around 60-63c all cores under 100% load from Cinebench). I played basically the entire night. I shut off my computer and went to bed.

 

I wake up this morning. LEDs from the motherboard are flashing and changing colours (Maximus X Formula has RGB lights all over it). I press the power switch. Nothing. Again. Nothing. I look to the I/O panel. The Bios flash button is not lit up (normally is green), but the RGB lights are working. However, although not lit, the clear CMOS I/O button does appear to have an effect, since pressing it causes the motherboard RGB lights to briefly shut off, before going back on again. It didn't seem to solve anything though.

 

I removed my new RAM, one by one. Did nothing. I removed my 1080 Ti. Still nothing. I then made sure that the 24-pin and 8-pin CPU connectors and cables made adequate contact. Sure. 
Once again, did nothing.

 

So, I am now wondering about the power supply. I had to RMA it around 4 months ago (in March), due to random shutdowns. The RMA took at least two weeks, which I don't have time for (I'm moving to Europe in mid August) and bringing my PC with me. It seems that AX860is have issues with failure rates. However, everything seemed fine last night. I had no shutdowns or anything of the kind. The self-power test for the power supply failed. The fans did not even spin nor did the red or green LEDs activate to say whether it failed or passed the test. All it would make was a faint click with each push of it. However, I had all of my cables connected to it when I tested, so that could be why.

 

The last thing I did last night after shutting my PC off was removing the power cable and putting a US/Canada to EU cable in place of it on the power supply, to see if the PSU end of it fit. It fit perfectly. The PC was turned off at this point. Is this simply a coincidence? 

 

Could it also be something with the motherboard (hopefully not fatal)? I had no indicators yesterday or whilst gaming the entire night that anything strange was going on. I could check again with the CPU 8-pin, since it is in an awkward location and theoretically could come loose or not make adequate-enough contact with the connector. The 24-pin, though, seems completely fine and sturdily placed.