Bizzare boot problems?! PC started by itself!

[samboy155]

Hey there!

Out of the blue my PC started not booting at all - no fans, no LEDS, nothing. Every now and again (let's say 1/10 attempts) I could boot it and it was fine but eventually that stopped working. Thinking it was the PSU I tried a new one - but same problem. Both passed paperclip test. Then I tried jumpstarting it using a screwdriver on the PW BTN pins which again OCCASIONALLY worked - until it didn't. Then nothing at all.

This is where it gets interesting...

I tried removing everything except CPU+Heatsink/Fan, new PSU and MOBO and still same problem. After getting sick of trying I put it in the shop where --->>>the guy said it was booting fine for him but wasn't getting any POST <<<--- said he "thought" it could be the CPU.. Took it home >>>and it booted every single time but without POST<<</"No input detected" on monitor (on both onboard and RX480 GPU) - same as the shop guy. I then reseated the CPU/Heat-sink and immediately began having the original no boot problem...


Asrock AB350 Pro4
Ryzen 5 1400

- Oh, in the beginning the few times it DID boot once it was running it had no problems, and CPU-Z reported no problems.
- No diagnostic speaker
- No pins on cpu are bent
- Fresh thermal paste applied at shop

CPU problem? MOBO? Any ideas? Thanks.

 

[ElectrO_90]

I'd say Motherboard, as there is a lot more to go wrong on that than a CPU.
If you still got the warranty, claim it back.
It should have a 3 year warranty.
If it turns out not to be that, then has to be CPU? Again that also has a warranty on it.

 

[samboy155]

I'd say Motherboard, as there is a lot more to go wrong on that than a CPU.
If you still got the warranty, claim it back.
It should have a 3 year warranty.
If it turns out not to be that, then has to be CPU? Again that also has a warranty on it.

Thanks for the reply. Gonna try find a cheap AM4 CPU to test it before sending it away..

Super interesting thing happened yesterday - after giving up on it for the night and going to bed, I woke up the next morning to find it ON!? WITHOUT THE CPU CONNECTED TO POWER AND WITHOUT THE PWR-SW connected?!?!
WTF. Anyway, I turned it off, reconnected everything and it started up AND POSTED - though it wasn't booting. BIOS was recognising the SSD was connected in the 'storage' section, but it was not appearing in boot devices. Weird.

I made a USB Repair and messed around with bootrec and diskpart and eventually got it repaired. Once I did everything worked find as though there wasn't a problem. Used this time to update the BIOS. For the rest of the day I was able to use the PC just fine and reboot/shutdown as often as I wanted no problem - though I never had it turned off for more than 5 minutes.

Skip to this morning... I wake up, press power button, anddddd same old no power/no boot problem. No fans, nada.

Wtf is going on? Does this mean it can't be the CPU?

 

[ElectrO_90]

I'm sure it is not the CPU but something weird in the motherboard.
When you look at a computer, there is not much in it.
CPU, Mobo, PSU, Ram, HD, GPU - You don't need the last 2 to boot it up so it is the first 4. Although it should turn on without ram, just act weird... so then that leaves us with 3... CPU doesn't normally break, which leaves 2. PSU or Mobo....

edit - unless the case has a switch fault.... then you need to use the screwdriver to turn it on which will bypass the case switch - as I have known switches to be faulty (this happened in my last build)

 

[samboy155]

I'm sure it is not the CPU but something weird in the motherboard.
When you look at a computer, there is not much in it.
CPU, Mobo, PSU, Ram, HD, GPU - You don't need the last 2 to boot it up so it is the first 4. Although it should turn on without ram, just act weird... so then that leaves us with 3... CPU doesn't normally break, which leaves 2. PSU or Mobo....

edit - unless the case has a switch fault.... then you need to use the screwdriver to turn it on which will bypass the case switch - as I have known switches to be faulty (this happened in my last build)

- Bought a second and tested PSU = not PSU
- Already ruled out the power button/cables. It wasn't even jumpstarting with screwdriver MOST of the time.
- Can't rule CPU just because it "doesn't normally break"; also as per my post the PC stopped powering up after reseating CPU (when it was previously after being returned from shop).

So at this stage I think its basically down to MOBO/CPU.. unfortunately can't find a used AM4 chip in my local area. Will keep looking.
Such a weird problem. Woke up again this morning, PC no boot. Came back 2 hours later and it booted first go np.

 

[samboy155]

Update for anyone still reading -

Taking it to the shop where the guy said it was booting first go got me thinking it could be my house's wiring. As it wasn't powering on at all at home, I took it to my sisters house and voila it booted completely first go, video output and all. I then take it home, and just like when I got it back from the shop, it booted there as well. Then I left it turned off for a couple of hours, and when I tried again it no longer booted.. So to me that sounded like a house problem.

So.. I went out and got a multimeter - all outlets outputting proper voltage. Huh. So THEN I went and got an Uninterrupted Power Supply (UPS) with AVS: UPS powered from outlet, PC powered from UPS. Still no boot. Okay so maybe its not getting enough current/amps from the mains outlet? ....then I tried UPS on battery mode (not plugged into outlet) with PC plugged into UPS -> NO BOOT?! The UPS should be outputting enough amps to run the PC when it's on battery mode right? So confused, surely the UPS should power the PC up... or maybe it doens't output enough amps to START a PC only enough to KEEP IT RUNNING?

Anyway, next step is to call an electrician to poke around the house wiring. Ughhhh.