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Solved No Power to MoBo/Strange PC Behaviour

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Hi all, I'm having a strange time with my PC and I'm hoping someone can help me.

A week or so ago I started having issues with turning on my PC. I figured it was just a loose connection between the motherboard and the power switch, since I had to resort to booting up using the power button on the Mobo. I managed to rearrange the pins correctly and it all booted up fine with the chassis switch, so I thought nothing of it.

A few days later however, I go to boot and suddenly there's no power at all going to the Mobo. No power LED light. I checked the socket, the extension it was plugged into, changed the fuse on the plug itself, checked connections, but there's simply no sign of life - No fans were spinning in the PSU which led me to believe it was to blame and possibly needed replacing.

I took it to a PC shop and explained my issues and that it may need a new power supply, and they quarantined it for a few days before taking a look. I get a phone call this morning saying that it just magically booted up for them. They didn't need to run any kind of diagnostic, and didn't charge me since they couldn't find a fault. It booted up, reset on command, and was running for them for three hours. They also tested the PSU and it came back green for them, so no issues there apparently.

I take it back home, plug it in and... nothing. No light on the motherboard. Same issue. So a bit of a mystery on my hands, here. I'd appreciate any help people can give me as I'd really like to try and fix this myself if possible, but if not, it looks like I'll be calling the shop again in the morning!

Thanks for reading. I don't have exact specs but I can try to recall them if needed. Hope you can help!
Hi, thanks for replying!

I certainly did, but no change. This morning however, I peer into my chassis and the power LED light is on. Hit the power button and, voila, it booted! I'm typing my reply from my main rig right now, but I'm not going to pretend it won't most likely do this strange behaviour again.

I have a few leads right now as to what's causing this. My first thought is that giving it time to cool off last night might have discharged any additional electricity which might have stopped it from booting. The other is oddly enough, the CMOS battery. Which is what I'm banking on. The reason why is when it loaded up, the time showed as yesterday, when it was getting serviced in the shop. Sign that it needs looking at or possibly resetting. While most people swear the CMOS battery has no bearing on a PC booting, I've found a few threads saying otherwise:

I'm happy to hear thoughts from more experienced folk though, I'm a self-taught novice when it comes to PC's at best (though I'd love to change that and become an apprentice technician to learn more) so any help is appreciated. I can't say I've cleared the CMOS or installed a new one before, so it'd be nice to know what to expect if I do. (Then there's the case of moving my chunky GPU out of the way so I can access it...)

My specs:

OS: Windows 10 Pro Activated
Processor: Intel(R) Core(TM) i5-7500 CPU @ 3.40GHz
Mobo: MSI Z270 Gaming M7
Ram: Corsair 16GB
GPU: NVIDIA GeForce GTX 1050
Drives: Samsung SSD 750 EVO 250GB
Seagate 1TB
Toshiba 2TB

Thanks again for reading.

Edit: link to other forum discussion removed
Last edited by a moderator:
Just to answer you question regarding the cmos battery. If you look at your motherboard you will see a button battery (a 2032) and if you remove this battery for 10 minutes your bios will reset to its defaults. Unlikely you will see any difference unless someone had been fiddling in there before. Whilst the battery is out take the opportunity to replace it.

FWIW chances are this is not your non booting problem, but as you asked about the battery the above is for your info.
Thanks for replying! I'm afraid I don't know the wattage or make of my PSU, but so far my problem seems to have just resolved itself and I'm still clueless as to why. It's booted fine for the past few days now, no problems. (It's currently plugged into the same socket with the same plug that it couldn't get power from before, yet here I am having it run 100% and typing on it just fine – no changes have been made at all, no extra switches flipped or wires changed etc.)

I do get an additional screen on boot however saying that all settings have been reverted to default - something I know to be from what's most likely a drained CMOS battery. (I've had this rig with same mobo for a few years now.) Thanks for the additonal info regarding the battery! To my knowledge it hasn't been touched or fiddled with, considering it's seated behind my GPU and the shop didn't take anything apart since it magically booted for them on their end. No changes needed to be made.

True mystery. If the problem reoccurs, I'll be sure to come back here and do more digging to get my PSU specs. (It was a hand-me-down of sorts so I'm having trouble finding any model or wattage label, and there's no online order or receipt details I can pull.) At present I've ordered a new set of batteries and plan to swap them out as soon as they arrive.

I know you guys haven't done too much regarding the situation, but thank you so much for being so willing to listen and to help. I'll be right back here if anything more strange and unusual happens. Again, thank you! Keep you all posted.
Thanks for letting us know, will close the thread but if you require assistance with this issue in the future please contact a staff member who can re open it for you.
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