New Ryzen 5 build does not boot randomly

[ammonia]

I have this new gaming PC I got two days ago. Since then there has been this booting problem. First time after assembling the whole system I started it up and it booted nicely and I got into UEFI. After checking all the details: RAM and CPU being correctly identified I started to install Windows 10. During the installation the PC will restart several times and when restarting, the computer restarts but will not post. After pressing reset button on the case front panel several times it posted again. I got Windows 10 installed and all the drivers too. Then I got Steam installed and PUBG. Game runs nicely.

Problem is whenever I shutdown the computer and then try to start it - it may post but in most cases it won't. What happens is that all the fans start spinning but keyboard lights won't light up and there is no picture on the screen. Then after pressing restart button enough it will eventually boot.

System specs:
PSU: Seasonic FOCUS+ 550W
CPU: AMD Ryzen 5 1600 (used)
RAM: G.Skill RipjawsV 2x8 GB 3200 MHz (used)
GPU: EVGA GTX 980 ACX 2.0 (used)
MB: ASRock AB350 PRO4.

Things tried:
- Another PSU
- Both RAM sticks in every slot
- CPU fan disconnected
- PC taken apart and rebuilt on table
- Memtest86+ being ran for 14 hours, 6 passes, 0 errors
- BIOS flashed to newest stable version
- BIOS flashed to beta version
- RAM speed lowered to 2400 MHz
- Fastboot disabled
- CMOS cleared

Which is more probable faulty motherboard or CPU?

TL;DR: Newly built PC works fine if gets past posting. Usually will not post and requires pressing front panel reset button several times.

Edit: after hours of fiddling and cursing I got the pc to post at least ten times in a row. I'm not even sure what all kind of settings I changed in BIOS but I lowered the RAM clockspeed to 2133 MHz. Is this an indication of a RAM issue?

 

[1LiquidPC]

I had similar issue last year with Ryzen 7 1700. This was even with Samsung B-die 3200 kit. You are likely failing memory training above 2133. The RAM itself is likely fine, the IMC in first-gen Ryzen is picky on modules. It will cause condition you describe, intermittent POST failures. However, when you can boot normally things are fine, including Memtest86. Is your RAM on the QVL for your motherboard? Your UEFI Is on latest version, as this greatly helped iron out these issues. You could try adjusting SOC voltage, or increasing DRAM voltage can fix the issue as well. There are many other possible memory tweaks, but they would require some research for your specific kit and board.

 

[ammonia]

G.Skills RipjawsV is not specifically in the ASRock QVL memory list but I know many people who have successfully used this kit in Ryzen build. Oddly enough I tried my friend's GTX650 on my PC and everything seemed to work perfectly. On the other hand my GTX980 seemed at first to work on his PC but then it suddenly started giving blue screen when loading Windows 10 and now his OS is unbootable because of corrupted boot image. I don't know if this was really caused by the GPU or not but at least nothing else changed in his setup as the problems started.

 

[1LiquidPC]

Strange, but could be a coincidence regarding GPU. Any changes with voltage?