Question PC won't turn on after unplugging it, what could be wrong?

[donnieberry]

3 days ago, I unplugged my PC to give it a clean. After plugging it back in, there was no power whatsoever. No LEDS, fans etc.

I tried resetting CMOS, taking the battery out for 10-15 seconds’ish, checking all cables etc.

Eventually, I tried once again plugging all my cables plugged into my pc externally and it turned on. Once it’s on, it’s completely fine, it can shut down and turn on again no problem. But I noticed that my bios has been reset and the time was wrong.

After doing some testing, it seems when I unplug my PSU from the power cable and then put it back in, the same issue occurs, the PC doesn’t turn back on but eventually will if I keep unplugging it and plugging it back in, and the bios is reset again. It can take 10 minutes, an hour, 2 hours etc.

What could this be?

It's worth noting that I had a technician test my PSU when he was diagnosing the PC and he said the PSU passes all his checks so it works completely fine. He put the issue down to a "motherboard short" but shortly after he left, the PC turned back on.

I've only had the motherboard for less than a year so I would be shocked if its anything related to it.

 

[Nine Layer Nige]

"I unplugged my PC to give it a clean",
Q: how did you actually go about that ?

 

[donnieberry]

"I unplugged my PC to give it a clean",
Q: how did you actually go about that ?

Sorry, should have explained.

Literally, I took the side panel off, realised it wasn't dirty really. So, I used a CompuCleaner to blow out the dust from the dust filters after removing them, and blew on the CPU fan a small amount (2-3 bursts of around 1-2 seconds) while holding my index finger on the fan to stop it from moving, that's it. Then I put the side panels back on.

 

[Zerk2012]

Since it's loosing the time first thing I would do is replace the battery on the motherboard.

 

[Bob.B]

3 days ago, I unplugged my PC to give it a clean. After plugging it back in, there was no power whatsoever. No LEDS, fans etc.

I tried resetting CMOS, taking the battery out for 10-15 seconds’ish, checking all cables etc.

Eventually, I tried once again plugging all my cables plugged into my pc externally and it turned on. Once it’s on, it’s completely fine, it can shut down and turn on again no problem. But I noticed that my bios has been reset and the time was wrong.

After doing some testing, it seems when I unplug my PSU from the power cable and then put it back in, the same issue occurs, the PC doesn’t turn back on but eventually will if I keep unplugging it and plugging it back in, and the bios is reset again. It can take 10 minutes, an hour, 2 hours etc.

What could this be?

It's worth noting that I had a technician test my PSU when he was diagnosing the PC and he said the PSU passes all his checks so it works completely fine. He put the issue down to a "motherboard short" but shortly after he left, the PC turned back on.

I've only had the motherboard for less than a year so I would be shocked if its anything related to it.

Cheap test.....replace the bios bat.

 

[dudio]

I'd start by replacing the cmos battery

 

[donnieberry]

Since it's loosing the time first thing I would do is replace the battery on the motherboard.

I held in the power button while the PC is off to drain all power, would that not cause the time to reset? (Sorry, I am a noob)

 

[Zerk2012]

I held in the power button while the PC is off to drain all power, would that not cause the time to reset? (Sorry, I am a noob)

Not if the battery was still in the board.

 

[donnieberry]

Not if the battery was still in the board.

Hmmm okay then. So what do you think? Once I removed the PSU cable, all power drained from the battery, stopping the system from turning on completely?

So what would make it turn on eventually?

Sorry for the questions, just trying to understand exactly whats going on here for my own knowledge!

 

[Nine Layer Nige]

Its possible, but not definite that by removing the CMOS, it reset the defaults on the BIOS which "may" have changed the ram timings to the default, which may have then caused the system to do some bootup thinking time whilst it learnt about the ram speed, perhaps. maybe, possibly.

 

[donnieberry]

Its possible, but not definite that by removing the CMOS, it reset the defaults on the BIOS which "may" have changed the ram timings to the default, which may have then caused the system to do some bootup thinking time whilst it learnt about the ram speed, perhaps. maybe, possibly.

Well, even when I got the PC working, unplugged it and plugged it back in, the issue reoccured. When the PC finally came back on, the bios was reset again, I didn't manually reset the CMOS or anything!

 

[Zerk2012]

Well, even when I got the PC working, unplugged it and plugged it back in, the issue reoccured. When the PC finally came back on, the bios was reset again, I didn't manually reset the CMOS or anything!

Replace the battery it's like 4 bucks. First and cheapest place to start.

 

[donnieberry]

The act of blowing dust around in PC can generate static. It can also create shorts.

>He put the issue down to a "motherboard short" but shortly after he left, the PC turned back on.

He's most likely right. Apparently, the short can be intermittent. The fact that the BIOS periodically resets itself is indicative of a short.

CMOS battery isn't likely suspect. CMOS draws power from PSU when PC is on, so unless PC was off for extended periods, batt doesn't lose power. Your issue started after said cleaning, so the act of cleaning is primary suspect.

>I've only had the motherboard for less than a year

Another indication that it's not battery.

Suggest removing MB & components from case, take them outside, and use canned air to completely remove dust. Take ESD precaution throughout.

Next, attach MB to PSU (and GPU if no iGPU present) outside of case, and try boot.

The motherboard was taken off by the technician as he wanted to check the front and back of it and inspect the case for any dust/damage. There was no dust around and the PC still didn't boot.

 

[donnieberry]

Visual inspection doesn't do much in detecting shorts/damage, unless a part is blown, which then you can smell the burnt odor before you notice the blown part.

Whatever the issue is, the cleaning action directly preceded it, and is thus most likely suspect. The ongoing behavior is indicative of a short. Take whatever action you see fit.

Just to clarify also, the PC has never been unplugged before. So, this could have been an issue waiting to happen.

I would be absolutely stunned if this was a short, as when I cleaned it, I didn't touch the motherboard, there was barely any dust from the PC when I blew it and I made sure none of it was still in the case afterwards.

 

[CodeConnoisseur]

Just to clarify also, the PC has never been unplugged before. So, this could have been an issue waiting to happen.

I would be absolutely stunned if this was a short, as when I cleaned it, I didn't touch the motherboard, there was barely any dust from the PC when I blew it and I made sure none of it was still in the case afterwards.

However unlikely, dusting the motherboard could have dislodged something tiny and conductive which proceeded to bridge some connection. But that's just trying to explain the technician's findings, you should absolutely try following what others have said by breadboarding and replacing the CMOS battery first.

 

[donnieberry]

However unlikely, dusting the motherboard could have dislodged something tiny and conductive which proceeded to bridge some connection. But that's just trying to explain the technician's findings, you should absolutely try following what others have said by breadboarding and replacing the CMOS battery first.

>I would be absolutely stunned if this was a short...

"It's not my fault" is a typical response. You should put ego aside and focus on resolving your problem.

You've gotten a number of suggestions thus far: replacing battery; remove setup from case, clean, and bench test; or--to add one more--replace motherboard.

You should take action, as being defensive won't get you far. Suggest trying cheapest option first.

Replace the battery it's like 4 bucks. First and cheapest place to start.

Replaced the battery, the issue remains!

Although, a couple of times when I turned it off and unplugged it, it turned back on right away.. but after the 2nd or 3rd time, same issue occured. Wouldn't turn on and when it did, the BIOS was reset.

I was pressing the power button many times, but whats weird is, when I unplugged everything again, it turned on right away?

But, I've used that trick before and it didn't work.

 

[CodeConnoisseur]

Replaced the battery, the issue remains!

Although, a couple of times when I turned it off and unplugged it, it turned back on right away.. but after the 2nd or 3rd time, same issue occured. Wouldn't turn on and when it did, the BIOS was reset.

I was pressing the power button many times, but whats weird is, when I unplugged everything again, it turned on right away?

But, I've used that trick before and it didn't work.

The inconsistency is probably due to electrical transients (e.g. in capacitors) throughout the board which you are discharging when you unplug it. An otherwise unstable system can be made to work temporarily if there is initially no residual power, then proceed to fail catastrophically after being powered for some time. Take out the motherboard and physically inspect everything, breadboard if you haven't already, but it will probably need replacement or advanced repair.

 

[sitehostplus]

Replaced the battery, the issue remains!

Although, a couple of times when I turned it off and unplugged it, it turned back on right away.. but after the 2nd or 3rd time, same issue occured. Wouldn't turn on and when it did, the BIOS was reset.

I was pressing the power button many times, but whats weird is, when I unplugged everything again, it turned on right away?

But, I've used that trick before and it didn't work.

Try replacing the motherboard and see what happens.