PC *somtimes* booting. $25 lttstore gift card if you can fix it.

[CassWest]

Hi. A few days ago I built a PC for my sister, it does not boot, no fan spin, no lights. Unless you're persistent and you get lucky, then it boots fine and everything is detected (it does not crash once it is turned on, it runs as it should).
I have taken it apart and rebuilt it three times, I'm a decently experienced builder, I am confident I didn't mess anything up, every cable is plugged in as it should be, nothing should be shorting, while the PC is on, it works as it should, ran Cinebench as well as a GPU intensive game, temps are very good, works as expected under load.
Edit: The PC will start, if you do nothing except pushing the power on button and unplugging it from the wall a couple of times, seems incredibly random. I did this ritual for 10+ minutes and it eventually started.

Things I have tried:

• Checked cables & rebuilt it
• Tested it on a workbench bypassing the case (made no difference, still did not start)
• Cleared CMOS
• Tested several combination of RAM sticks/slots
• Tested with/without GPU
• Inspected cables and connectors from PSU to the Motherboard
• Tested multiple different outlets in two different houses

I'm sure there are more things but my brain is fried, don't know what to do from here, I don't really have access to a different mobo/PSU.
Offering a slight carrot consisting of a $25 lttstore gift card to anyone who can fix this. Might straight up be a mobo issue and I'm SOL.

Exact specs of everything:
Lian Li LANCOOL 215
Gigabyte GeForce RTX 3060 WINDFORCE OC
Samsung 1TB 980
Corsair 750W RM750x (2021)
MSI PRO Z790-P WIFI DDR4, ATX
Noctua NH-U12S
Kingston 16GB FURY DDR4
Intel Core i5-12400F

Any suggestions appreciated, thank

TL;DR: PC works well, when it starts, 3% of the time.
 

[rriccc]

This might be several things;
RAM might be misplaced, which is unlikely considering you've reseated everything.
Outdated BIOS might be a reason for this to happen
Faulty PSU
Faulty MOBO
CPU not seated properly

You did say you don't have access to another MOBO / PSU, which is unfortunate because either of those is probably causing those issues.

[kartelious]

Flakey boot behaviour seems like a CPU and/or connection issue to me.

When you rebuilt the PC, did you re-seat the CPU? if so was the thermal paste application sufficiently spread for even cooling of the IHS?

Also make sure that there are no bent pins or any shmoo in the socket.

(assuming youve got more thermal paste to hand)

[LHJKO]

What about powering it down via the power button does that work fine every time? It being perfectly fine once you do get it started seems like a connection issue with the power button or the connection on the board. 

 

I have def never had that happen before strange. 

[ToboRobot]

Intel F CPUs don't have iGPUs so the testing without a GPU just resulted in the computer failing to power on at all?

 

Presumably you have another computer, and can pull the PSU and test it in this system?  This is the most likely cause of this sort of issue and is easier than testing a different mobo?

 

[tkitch]

does it start if you jump the 2 pins with a screwdriver, and bypass the power button? 

[leclod]

8 minutes ago, LHJKO said:

What about powering it down via the power button does that work fine every time? It being perfectly fine once you do get it started seems like a connection issue with the power button or the connection on the board.

I'd say the contrary :It being not fine too seems like a connection issue with the power button or the connection on the board.

[LHJKO]

3 minutes ago, leclod said:

I'd say the contrary :It being not fine too seems like a connection issue with the power button or the connection on the board.

I am so confused what this is trying to say. 

[leclod]

1 minute ago, LHJKO said:

I am so confused what this is trying to say. 

I think you conclusion was wrong. If the power off works fine then the power button works.

[CassWest]

15 minutes ago, LHJKO said:

What about powering it down via the power button does that work fine every time? It being perfectly fine once you do get it started seems like a connection issue with the power button or the connection on the board. 

 

I have def never had that happen before strange. 

Yeah you can power it down as usual. It works fine when it's actually on.
 

 

6 minutes ago, tkitch said:

does it start if you jump the 2 pins with a screwdriver, and bypass the power button? 

It does not, I tried this several times.
 

 

26 minutes ago, kartelious said:

Flakey boot behaviour seems like a CPU and/or connection issue to me.

When you rebuilt the PC, did you re-seat the CPU? if so was the thermal paste application sufficiently spread for even cooling of the IHS?

Also make sure that there are no bent pins or any shmoo in the socket.

(assuming youve got more thermal paste to hand)

I was absurdly careful when I installed the CPU, I also checked all the pins on the mobo. The PC also runs as it should under 100% load with Cinebench, I have the Noctua cooler on a very quiet setting and it still didn't go past 50c in a hot room under full load, I doubt it's the CPU, I did not yet re-seat it.  
edit: would I get fan spin/lights if it was a CPU issue?

[LHJKO]

1 minute ago, leclod said:

I think you conclusion was wrong. If the power off works fine then the power button works.

Yeah thats why I was asking if the power down works fine everytime.

[CassWest]

7 minutes ago, ToboRobot said:

Intel F CPUs don't have iGPUs so the testing without a GPU just resulted in the computer failing to power on at all?

 

Presumably you have another computer, and can pull the PSU and test it in this system?  This is the most likely cause of this sort of issue and is easier than testing a different mobo?

 

I would imagine I can still power it on even without a GPU, there wouldn't be any display out but I could still see fan spin/lights.
And yeah I can, but I need my other pc for work i haven't had the time to pull it out yet.

[PaulHubers]

2 minutes ago, CassWest said:

Yeah you can power it down as usual. It works fine when it's actually on.
 

 

It does not, I tried this several times.
 

 

I was absurdly careful when I installed the CPU, I also checked all the pins on the mobo. The PC also runs as it should under 100% load with Cinebench, I have the Noctua cooler on a very quiet setting and it still didn't go past 50c in a hot room under full load, I doubt it's the CPU, I did not yet re-seat it.  

Have you tried a single stick of ram and rotating to different sticks to see if the issue continues?

[leclod]

3 minutes ago, LHJKO said:

Yeah thats why I was asking if the power down works fine everytime.

Ok,

Wasn't that "It being perfectly fine once you do get it started seems like a connection issue with the power button or the connection on the board.  " a complicated sentence though ?

Edited July 26, 2023 by leclod

[rriccc]

5 minutes ago, CassWest said:

Yeah you can power it down as usual. It works fine when it's actually on.
 

 

It does not, I tried this several times.
 

 

I was absurdly careful when I installed the CPU, I also checked all the pins on the mobo. The PC also runs as it should under 100% load with Cinebench, I have the Noctua cooler on a very quiet setting and it still didn't go past 50c in a hot room under full load, I doubt it's the CPU, I did not yet re-seat it.  
edit: would I get fan spin/lights if it was a CPU issue?

I'm pretty sure you'd get fan spins even if it was a CPU issue. If they weren't spinning, it would most likely be a mobo / PSU issue.
As @leclod said, your best bet would be testing a different PSU.

[CassWest]

1 minute ago, PaulHubers said:

Have you tried a single stick of ram and rotating to different sticks to see if the issue continues?

Yes, the issue persists even with RAM in different slots.

[Agall]

1 minute ago, CassWest said:

Yes, the issue persists even with RAM in different slots.

I'd check the 24pin to ensure that none of the pins are damaged, the cable and motherboard side port. Mostly checking to see if any of the 24 pins in that connector didn't pull out or such.

[CassWest]

Just now, Agall said:

I'd check the 24pin to ensure that none of the pins are damaged, the cable and motherboard side port. Mostly checking to see if any of the 24 pins in that connector didn't pull out or such.

Yeah I did inspect all cables and connectors. I even took pictures to send to a friend, nothing out of the ordinary. I also feel like a damaged connector would not allow the PC to work at all.

[Agall]

1 minute ago, CassWest said:

Yeah I did inspect all cables and connectors. I even took pictures to send to a friend, nothing out of the ordinary. I also feel like a damaged connector would not allow the PC to work at all.

One or two of the pins not fully seated in the connector could create some strange behavior like that, and/or with intermittent connectivity. You can also short test the power supply to make sure it turns on properly with a paper clip.

[Robchil]

1 minute ago, CassWest said:

Yeah I did inspect all cables and connectors. I even took pictures to send to a friend, nothing out of the ordinary. I also feel like a damaged connector would not allow the PC to work at all.

i would check or replace the cables between psu and mainboard.. sounds like one pin isn't properly plugged in.. 

[PaulHubers]

9 minutes ago, CassWest said:

Yes, the issue persists even with RAM in different slots.

Okay, also adding on from what other people have already said. I would try another PSU and double check that no pins are bent where the CPU seats. If the pins are good and the different PSU doesn't fix it I would have to think the board is the culprit.

[CassWest]

1 minute ago, Agall said:

One or two of the pins not fully seated in the connector could create some strange behavior like that, and/or with intermittent connectivity. You can also short test the power supply to make sure it turns on properly with a paper clip.

RMAing the PSU might be an easy first step to try. It's brand new Corsair PSU so you'd think it would work though. 

[CassWest]

2 minutes ago, PaulHubers said:

Okay, also adding on from what other people have already said. I would try another PSU and double check that no pins are bent where the CPU seats. If the pins are good and the different PSU doesn't fix it I would have to think the board is the culprit.

Would I not get fan spin/lights from something even if the CPU wasn't properly installed? Also I inspected the pins on the motherboard before very carefully installing the CPU, It's a good shout but I don't think the CPU is the issue.

[Agall]

Just now, CassWest said:

RMAing the PSU might be an easy first step to try. It's brand new Corsair PSU so you'd think it would work though. 

DOA parts happen all the time, so do defective parts within the first few months. Ideally you're able to isolate the faulty component with spare parts or individual troubleshooting, short starting the PSU will tell you if its working properly.

 

The PSU stays on because there's one pin connected to ground, usually pins 4,5 being how I describe it.

 

 

Some PSUs come with a tool for doing this that's just a female connector configured as such. They're also useful for custom loops where you'd need to run a pump. Doing it with a paperclip as shown is a legit method, I even have an old power supply configured as such for SATA/MOLEX power for various things, including modified machinery to add fans.

[PaulHubers]

4 minutes ago, CassWest said:

Would I not get fan spin/lights from something even if the CPU wasn't properly installed? Also I inspected the pins on the motherboard before very carefully installing the CPU, It's a good shout but I don't think the CPU is the issue.

I have heard of it happening both ways, even Linus in videos has mentioned that they have had systems have boot issues or intermittent issues due to a pin not making full contact on the board. It is a stretch for sure but you never know sometimes.