Need help, PC turns on then immediately off.

[xenonpotatoes]

My fairly new PC, built it about 2 months ago, is not turning on properly. I just re-cable managed and put in a new hard drive. It'll turn on, the lights will come up, then it'll turn off about 1 second afterwards. It'll keep turning on then off unless I just cut the power. I've tried everything I could think of and that I've found online.

Specs:
i7-7700k
NZXT Kraken X62
Gigabyte Z270X Designare
Trident-Z RGB 3000mhz
EVGA 1080 Ti SC2
Samsung 850 Evo 500GB SSD
2 TB Seagate HDD
Corsair RM750x
S340 Elite

From all that I've tried, I can only think that it's PSU failure.

 

[1LiquidPC]

Everything worked correctly until the added HDD and cable management? If so, have you tried removing power to the drive to test? Possible short caused somewhere by a loose pin in connection.

 

[xenonpotatoes]

Everything worked correctly until the added HDD and cable management? If so, have you tried removing power to the drive to test? Possible short caused somewhere by a loose pin in connection.

Yes, everything worked until I added the HDD and re-cabled. I tried removing power to the drive, I even tried just fully removing it. I've also removed the mobo to check for loose screws that may cause shorts, I've reseated the cooler, I've reseated the RAM and GPU. I'm fairly sure that all the power cables are fully connected and that any other connections to the motherboard are okay.
I may try removing the CMOS battery, as I've seen other websites recommend, or reseat the CPU.

 

[1LiquidPC]

I'd retrace all your steps for the hdd upgrade and cabling. Seems highly unlikely to have a hardware failure at same time being unrelated. Regarding connections, are you sure the pins inside the connectors themselves are fully seated? Its possible one didn't mate correctly in 24pin or 4/8pin for example.

 

[jonnyguru]

You're only using the cables that came with the PSU, right?

They all say "Type 4" where they plug into the PSU?

 

[xenonpotatoes]

Yes, I'm sure the cables are fully seated, I'll recheck to make sure. And yes, they all say type 4 when connecting to the PSU.