PC won't turn on unless hard restart (disconnect and connect the power cord realy guickly)

[AndreyD]

Hi everyone, I build my PC in 2018 and it's been rock solid for the first 2 years but numerous problems started occurring about a year ago. All components remained the same but it would randomly blue screen on me regardless if I stress test the PC or not.
I found out that down clocking the RAM from its default 2400MHz to 2133MHz for whatever reason solved the issue.
When I upgraded the 8gb of RAM to a new kit of 2x8gb Kingston KVR26N1928/8 the system worked just fine on the default 2666MHz (XMP) so I figured out that the old RAM module was to blame, boy was I wrong.

After a couple of weeks the PC was stable this time (no blue screens) but boot problems started to occur:
1. In the beginning the PC wouldn't wake up from sleep. During wakeup the fans would ramp up to 100%, no video and no response on the power or reset button, nor removing the power cord helped (same boot to black screen). The only method that worked was to unplug and replug the power cord in 0.5s and after that it would boot normally
2. After some time the boot issues started occurring even after completely shutting down the PC
3. Some time after that the boot issue was present after every shutdown or sleep and the above method for solving it worked every other time
4. The final coffin was days ago when it finally booted and I got a video signal the PC would display the "insert bootable drive and press any key" message and after a couple more tries of replugging the power cord it booted

 

My boot drive is a Samsung 860 EVO 500gb so this is not the problem, I know that Ryzen 1. gen had RAM issues but it should have been solved on the 2600x. 
Other things I tried was updating the BIOS, reinstating the RAM sticks in different slots (they are in A2/B2 as per the mobo manual) and removing USB devices. One time I noticed that one case fan was not running and after unplugging it the PC would boot normally for a day or two and then back to the start. Anyone have any ideas?

 

PC specs:
CPU - Ryzen 2600x
RAM - 2x8gb Kingston KVR26N1928/8
Mobo - Asrock X470 Gaming K4
PSU - Cooler Master B700
GPU - Inno 3D GTX 1070ti
Case fans - Thermaltake Riing 12