New Build Won't Turn On.

[boltie]

New build pc turns of for 1 second then turns off. Was working fine yesterday and for 20 minutes today. Then it just turned off and now won't turn back on. Or it powers on for a brief moment (around 1 second) then just powers off again, and after that it won't even power on until I replug the power cable back into it.
I've Tried checking all connections and taking all the parts out and putting them back in again, including RAM. Reset CMOS, as well as just trying to turn the system on with just the necessary components, however no luck. So I'm thinking it may be the PSU?

I've already checked several forums and youtube videos etc, still no luck.

I've already contacted the place where I bought the PSU, however is there anything else I should / can check?

Any help would be appricaited.

SPECS:

NZXT H440 New 2015 Edition Case - Matte Black & Red
Asus ROG Strix Z370-H Gaming Intel Z370 (Socket 1151) DDR4 ATX Motherboard
Intel Core i7-8700K 3.7GHz (Coffee Lake) Socket LGA1151 Processor - Retail
Kingston HyperX Predator 32GB (2x16GB) DDR4 PC4-21300C13 2666MHz Dual Channel Kit (HX426C13PB3K2/32)
GeForce GTX 1080Ti Gaming X 11264MB GDDR5X PCI-Express Graphics Card
Crucial MX300 525GB SSD M2 2280 6Gbps 3D Nand Solid State Drive (CT525MX300SSD4)
WD 6TB Black Internal Performance Hard Drive (WD6002FZWX)
Corsair HX750i 750W '80 Plus Platinum Digital Modular Power Supply (CP-9020072-UK)
TP-Link AV1000 2-Port Gigabit Passthrough Powerline Starter Kit (TL-PA7020P KIT)

 

[DRagor]

Check other power cable/other wall socket. If that won't help, first suspect is PSU, with motherboard being second (but much less likely).