Weird PC boot problem

[Dalea]

My PC decided to stop booting today, however, I could not find a post anywhere with symptoms similar to mine, thus I am reaching out for help.

 

Issue: The PC turns on and immediately shuts down, powers up by itself and keeps running, however, the power flickers for a fraction of a second every 3 seconds or so, when the fans and lights turn off but then fire back up immediately. It keeps running, but booting doesn’t happen. I have attached a video. FYI: The orange light on the mobo is not an error light - just a design feature. My guess is that it’s either a PSU or Motherboard failure, however, maybe there is something I have missed, and the solution is simple.

 

Things I’ve done:

• Tried a new power cable for the PSU
• Did a BIOS reset by removing CMOS battery
• Tried booting with 4 different RAM sticks 1 by 1 in both slots
• Tried 2 different GPUs
• Reseated the CPU
• Reseated all the connectors
• Tried booting without GPU
• Tried breadboarding

 

Specs:

• CPU: Intel i5-9600k
• GPU: AMD Radeon RX 6600 8gb
• RAM: Corsair Vengance LPX 2x8GB DDR4
• MB: Gigabyte B365M HD3
• PSU: Be quiet! 600W (80 Plus Gold)
• SSD: 2 x Kingston A400 SATA SSD 240GB
• CPU Cooler: DeepCool AK400 ZeroDark
• Windows 11 Home 64-bit

 

Any help will be appreciated!

[Allan B]

I think you have narrowed it down fairly well.   You have eliminated GPU, RAM, connections, etc...

 

You are down to the MB, PSU or CPU.  It is unlikely the CPU has failed, I would suggest the PSU next as it is the most likely and easiest thing to replace.  Note:  do not reuse any PSU cables if your current PSU cables are modular.

If possible try a spare or borrow a PSU to test, if you can.

[StDragon]

I second that as well, swap the PSU

[FreddyWestside]

I've seen this before but it's been years and can't remember exactly what the causes were. It could be a completely borked bios that's just stuck in a loop before the post screen or the bios is set to automatically turn on after a power failure and the PSU is cutting out.

[Allan B]

23 hours ago, FreddyWestside said:

I've seen this before but it's been years and can't remember exactly what the causes were. It could be a completely borked bios that's just stuck in a loop before the post screen or the bios is set to automatically turn on after a power failure and the PSU is cutting out.

It is a good point, you could also try removing the bios battery on the motherboard and disconnect the PC from the wall (no power at all).. wait 10-15 minutes and try to power it up..