Short answer
There are two different behaviours here: Windows crashing and restarting itself, and the machine losing power outright. Turning off automatic restart tells you which one you have, and that decides where to look next.
Two behaviours, two different causes
- Windows crashes and restarts — a blue screen happened but the machine rebooted before you could read it. Windows does this by default.
- The machine loses power instantly and comes back — no crash was logged, because nothing had time to log it. Power, heat or a protection trip.
- The machine restarts on a schedule or after an update — Windows Update, a scheduled task, or a driver installation. The least worrying version.
- 1
Turn off automatic restart
System Properties, Advanced, Startup and Recovery, then untick "Automatically restart". Next time it happens you will either see a blue screen — which changes this into a stop-code investigation — or the machine will still reboot instantly, which points at power.
- 2
Check Event Viewer
In the System log, Kernel-Power event ID 41 means the machine went down without a clean shutdown. A BugCheck entry means Windows crashed and recorded it.
Possible causes
| Cause | Pattern that suggests it |
|---|---|
| Power supply | Restarts under load, when a printer or heater on the same circuit kicks in, or increasing with the unit's age |
| Wall power | Other devices in the room flicker too; the machine is on a surge strip shared with heavy appliances |
| Overheating | Restarts after several minutes of use, fans loud, case hot, dusty machine |
| Memory | Random restarts plus occasional blue screens and file corruption |
| Storage | Restarts during file access, plus freezes, long stalls or missing files |
| Drivers or Windows | Started right after an update; usually accompanied by a logged crash |
| Malware | Restarts alongside popups, browser changes, unfamiliar software |
| Loose internal connections | Started after the machine was moved or worked on |
| Failing motherboard | Everything else tests clean and it still happens |
What you can check safely
- 1
Plug straight into the wall
Bypass surge strips, extension leads and UPS units for a few days. Failed strips are common and free to rule out.
- 2
Log temperatures
Use monitoring software that writes to a file and check the last readings before a restart.
- 3
Clean the dust out
Unplugged, clear filters, heatsink fins and fan blades. Confirm every fan spins during use.
- 4
Test memory overnight
Any error means the memory configuration is not stable.
- 5
Check drive health and free space
Look at SMART status and make sure the system drive is not nearly full.
- 6
Scan for malware
Run a full scan with a reputable tool, particularly if the restarts came with popups or unfamiliar programs.
- 7
Undo recent changes
Roll back a driver installed just before the trouble started, or uninstall a recent Windows update if the timing lines up.
- 8
Return to stock
Disable overclocks and memory profiles.
What each result may indicate
- A blue screen now appears — you have a stop code to work with; move to the blue screen guide.
- Kernel-Power 41 with no crash logged — the machine lost power. Look at the supply, the outlet, thermals and connections.
- Restarts stop on a different outlet — the original circuit or strip was the problem.
- Restarts only under load — power delivery or heat.
- Restarts at idle as well — less likely to be thermal; power, memory or the board move up.
- Memory errors — resolve those before considering anything else.
Protect your files
When to stop DIY
Stop if the restarts come with burning smells, drive noises, visible damage, or if the machine starts failing to come back up. Stop as well when the next step is buying a power supply or memory speculatively.
When to bring it in
Random reboots are exactly the fault class that bench substitution solves fastest: a known-good supply on the same machine settles the biggest question in an afternoon. Bring it to the shop in Bellevue and tell us the pattern you noticed — that information genuinely shortens the work.
Common questions
- My PC restarts only when I'm gaming. Is it the graphics card?
- It might be, but load-related reboots more often come from power delivery or heat. The card is one of several suspects, not the obvious answer.
- Can Windows Update cause random restarts?
- Scheduled restarts after updates are normal and predictable. Random restarts at any hour are not, even if they started after an update — in that case, a driver from that update is the thing to look at.
- Could a virus make my computer restart?
- It can, though it is less common than power or heat. If there are also popups, browser changes or unfamiliar software, treat malware as a real possibility.
The service that covers this
Computer Diagnostics & Repair
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