how do I fix a PC that isn't successfully passing POST?

[Loumier]

Hi, guys. I've that PC (specs at the end of the post) that has a problem with Post.

Randomly it just doesn't turns on, I really don't know why. I didn't touch any components, didn't change any BIOS settings, and it just doesn't turns on properly. It almost turns on, all the lights and fans turns on, but doesn't has any video output. With any, I mean literally any, often when I say that people misunderstand by it shows the system boot screen but after that has no video output. That means even the Setup screen isn't shown, meaning I can't even access BIOS setup. Also, it keeps stuck into a reboot loop, the PC is on for a few seconds then reboot.

That already happened many times, and everytime that happened after some minutes or hours it randomly just boots up like if nothing happened and works normally. Odd, hm?

Last time that happened in a try to diagnose the issue I took my PC to my work (I work with computer maintenance) where I could find some parts to test out my PC. I replaced all my parts for other perfectly working parts, except for the Mobo because I couldn't find other LGA 1155 Mobo. After replacing every part the problem remained. Then I gave up, took my PC back to my home and guess what? The next day I tried to turn on and it just turned on.
I also already tried to clear the CMOS and move the jumper position.

My setup:
Intel I7 3770 (no K, overclock locked)
2x 4Gb Corsair Vengeance LP 1333Mhz
EVGA GTX 970 4Gb
Motherboard Asus P8-H77M
PSU Aerocool 500W Bronze+
1Tb Seagate Barracuda 7200rpm Sata 3
120Gb Samsung Evo 850 Sata 3

 

[camieabz]

Remove gfx card and RAM, give the contact edges a clean (google best ways to do this), and re-seat firmly, ensuring locking clips pop in properly.

Double check all direct PSU connections from PSU to gfx card (2 x 6 pin I think) are made and secure. Then double check that any additional PSU to mobo connections are made and secure. Now disconnect all drives and fans, except CPU fan (or pump if applicable).

If that doesn't help, you need to get your hands on another PSU, ideally a more beefy one, to eliminate your PSU as the culprit. Keep an eye on the CPU cooler for anything that suggests it's not working as expected. Get into BIOS and check temps if necessary. See how things go with that.