PC boot and shutdown issues

Hey everyone.

I'm dealing with a double whammy on my PC. I've spent hours scouring the web and trying every fix I could find, but nothing's sticking, so I'm turning to you guys as my last resort. 😁

Issue #1:

For a few days now, my computer hasn't been booting properly. I hit the power button, it starts the boot sequence, and then—bam—it just shuts off. I even opened it up and cleaned out all the dust, but no luck. To cut to the chase, I noticed that if I leave the ethernet cable unplugged, it boots up perfectly fine. But if I plug that cable in before I hit the Winlogon screen, the whole thing just dies. If I wait until I actually reach Winlogon to plug it in, it runs smooth as silk. The motherboard light stays lit, there aren't any weird noises, and I've run all the standard diagnostics—HDD and RAM both check out fine. I even swapped out the cable, but it still kills the system if it's plugged in during bootup. 😠

Issue #2:

At the same time, I'm having this weird restart loop. About five seconds after I shut the PC down, it just restarts itself automatically. In this case, having the ethernet cable plugged in doesn't seem to trigger it. My only workaround is to pull the power cord from the wall, wait about 20 seconds, and then plug it back in; otherwise, it just keeps rebooting instantly.

The internet says it's usually either hardware (like the motherboard or the power supply) or software (viruses or bad drivers). When it’s actually working, though, it runs like a dream.

Any ideas? Help me out. 🙂

To start things off, if I were in your shoes, I’d just wipe the hard drive and do a clean install of Windows—mostly just to be 100% sure we aren't dealing with some weird software glitch. Personally, though? My gut tells me it’s either the motherboard or the power supply. If a fresh OS doesn't fix it, you're basically looking at swapping out parts one by one... there really isn't much of another way to go about it, is there?

Daniel Ward87 said:Hi there!

I’m dealing with a bit of a double whammy with my PC, and honestly, I feel like I've exhausted all my Google searches and tried just about everything I could think of, so I figured I’d turn to this community as my absolute last resort. 😁

First issue.

For the past few days, my computer has been acting incredibly strange during the boot process. Basically, I hit the power button, it starts to boot up, and then—poof—it just shuts itself off completely. I even went ahead and cleaned out all the dust from the inside, but I guess that didn't change anything. To make a long story short, I noticed something really peculiar: if I don't have the Ethernet cable plugged in, it boots up perfectly fine without any drama. However, if I plug that cable in before I reach the Winlogon screen, the computer just shuts down automatically. If I wait until I see Winlogon and then plug it in, it works absolutely beautifully. The motherboard light stays lit constantly, I don't hear any weird noises, and I've run all sorts of diagnostics, but nothing shows any errors with my SSD or RAM. I even swapped out the cable entirely, but it seems like it doesn't matter—if it's connected during the boot sequence, it just dies. 😠

Second issue.

At the exact same time, I'm having this weird situation where, after I shut the computer down, it decides to restart itself about five seconds later. In this specific scenario, having the Ethernet cable plugged in doesn't seem to trigger it. Every single time this happens, I have to physically unplug the power cord from the wall and wait maybe 20 seconds before plugging it back in, otherwise, it just keeps looping into a restart immediately.

I've read all sorts of things online suggesting this might be hardware-related (like the motherboard or the power supply) or software-based (maybe a virus or some buggy drivers), but when it actually functions correctly, the machine runs like an absolute dream.

So, yeah, please help me out if you can! 🙂

Maybe try checking your BIOS to see if there are any settings enabled like Wake on LAN, or any weird WiFi checks or similar features that might be triggering these power cycles.

It would also probably be super helpful if you could let us know which motherboard you're using.😁

Quick recap here.

Turns out the power supply was the culprit behind everything. Two capacitors had swollen and corroded, which basically caused the motherboard to lose its mind. I saw someone on a tech forum mention a similar issue where a faulty PSU causes the motherboard—likely via the BIOS—to trigger a reboot during shutdown. Apparently, it’s a built-in safety measure because there's a risk the PC won't boot back up if it shuts down improperly. I'm no expert, just passing along what I read.

Anyway, I picked up a new power supply and some fresh components, so I've basically got a semi-new rig now. The old motherboard is still running fine; we tested it with a different PSU and the Ethernet cable isn't acting up anymore.

Thx everyone.

Quick recap here.

Basically, the power supply was the culprit. Two capacitors had swollen and corroded, which is why the motherboard was acting totally haywire. I saw someone on a tech forum mention a similar situation where a faulty PSU caused the motherboard—likely through some BIOS setting—to trigger a system reboot during shutdown. Apparently, it's a sort of failsafe to ensure the PC can actually boot back up once it's turned off. I'm no expert, just passing along what I read.

Anyway, I picked up a new power supply and swapped in a few fresh components, so I’ve basically got a semi-new rig now. The old motherboard is still running fine; we tested it with a different PSU and the Ethernet connection is perfectly stable.

Thx everyone.

Better late than never, though I suppose an explanation was overdue

System shutdowns are frequently the result of a failing power supply unit; a quick diagnostic involves simply disconnecting the power to the optical drive. In almost every scenario—barring a cold solder joint—the culprits are capacitors that have lost their capacity. This prevents the switching power supply from maintaining steady voltages, which inevitably triggers a shutdown. The telltale sign is having to repeatedly attempt to boot the machine (or any electronic device, really) until it stabilizes momentarily, only for it to overheat and crash during extended use.
The logic behind this isn't entirely sound either, as the initial shutdown reduces the load, allowing voltages to reset to acceptable levels. Furthermore, transient phenomena on pin 16 (the green wire) can sometimes ground the potential enough to trick the motherboard into starting again. It sounds counterintuitive, I realize, but think of it like a swing gaining momentum through repetitive motion.
It is advisable to shut down your computers completely—using the switch on the power strip, for instance. Even in standby mode, the primary capacitors remain fully charged, which shortens their lifespan. Beyond longevity, you might even save a few bucks on your monthly utility bill.
Even Ethernet communication consumes a measurable amount of power, and it seems that was the final straw that pushed the system over the edge.