Question Black Screen only after restarting PC ?

Feb 5, 2021
First, my PC broke when my brother attempted to "clean" it. After cleaning, my PC won't boot anymore. I was away from home for a long time that's why I wasn't able to check what he did. When I got home, I tried to reseat everything, replaced CMOS, boot without the GPU, but no luck.

I brought it to a tech shop and found out that the PSU was the culprit. I bought a new PSU, replaced it, and started to boot again. Until a few hours passed, my PC started booting automatically to a black screen. No cursor. Just black screen. The lights, fans, keyboard and mouse shows that they are working (lights on, fans running). Also, the monitor is on, as shown by the light indicator. What I did was, I pressed the power button to turn the pc off. Then turn it back on. It boots normally when I do that. But when I try to restart my pc manually, it also goes back to black screen. Then I just turn it off and on again. It's still restarting automatically a few minutes after logging in to the desktop.

I checked the BIOS for some anomalies, found out that the 5V is in red, and is showing 8.6V. I knew then that this is what's causing all the problems. Also used HWMonitor, the same reading is shown. Tried to check it back again the next morning, still red, but around 7.4V. I tried to disconnect everything from the PSU, starting with the fans, GPU, etc. I also tried booting without the GPU, the same thing. Still at ~7V.

I had the newly bought PSU replaced with a new one, nothing changed, still showing a red 5V at around 6-7V. It's still restarting to black screen automatically, and also going to black screen when I restart manually. In the BIOS, I tried to ignore the 5V, now it stopped restarting automatically. But still when I restart manually, it goes to black screen. I tried DIY troubleshooting, like pressing Win+Shift+Ctrl+B during black screen, and other keys. Not helping. I tried to reinstall the Windows 10, updated all the drivers, reseat PSU connectors, boot with and without GPU, reseat RAM, CMOS, Storage devices, reconnected and swapped HDMI and DisplayPort, etc. Nothing changed. Also, the audio devices are not being detected when I connect it at the rear and front audio jacks.

Note that all drivers are updated to the latest. I can play games though. I just prefer not to until the problems are fixed. I'm also using the audio from my monitor. After doing all that, I tested the PSU using an analog multimeter. Everything was connected, except for 1 fan to a 4-pin Molex where I did my testing. I contacted the negative needle (black) to the ground (black in 4-pin) and positive needle (red) to the 5V (red in 4-pin). It's showing an exact 5V. So I thought maybe the sensors, nay, the motherboard is faulty. But I'm not really sure with that. I also think maybe the GPU is faulty. But the thing is, I can play games with no problems. No video/screen glitches. During black screen after manual restart, windows sounds play, meaning that it did boot, just that there's no display.

I don't have any other units or extra components to check everything. My friends live far away so I can't use their setup to check mine.

My questions are:
  1. Is there a way to fix the 5V showing high voltage?
  2. Can I continue using my PC (5V in BIOS is ignored) even though it has this problems?
  3. What's causing the black screen after manual restart?
  4. Why is it automatically restarting to black screen when 5V in BIOS is not being ignored?
  1. In BIOS, 5V is in red, showing as high as 8V. As of writing, 5.8V to 6V in the BIOS and HWMonitor.
  2. Normal startup, but will auto-restart to black screen. Auto-restart will stop when 5V is ignored in BIOS. But will go to black screen when manually restarting PC.
  3. I can play video games, watch videos, type this post with no problems/glitches.
  4. Audio devices are not being detected even when devices are connected. I'm using monitor's audio.
CPU: Intel i7-7700
MB: Asus Prime B250M-D
GPU: Nvidia GeForce RTX 2060 Super 8GB
Memory: TForce TUF 2x8GB
New PSU: Gigabyte P650B 650W 80Plus Bronze
Storage: 1 SSD 500GB Samsung 860EVO, 1 HDD Western Digital Blue 1TB
Monitor: Asus VP249QGR 24in
4 case Fans, No RGB LED Strips