Why does my computer keep restarting on its own?
A machine that reboots without asking is telling you something specific. How to tell an update from an overheat from a failing power supply, using the log the computer has already written.
- Difficulty
- beginner
- Time
- 25 min
- Read
- 5 min
Short answer
Check the timing first: restarts that happen overnight or after you leave it are almost always updates, and restarts under load are almost always heat or power. Windows records every unexpected shutdown in Event Viewer and macOS records panics in the system log, so the machine has already written down what happened — read that before changing anything.
There is an important distinction hiding in this symptom. A computer that restarts cleanly, showing a shutdown screen, has decided to restart — that is software, usually an update. A computer that simply goes off and comes back, as though the power had been pulled, has not decided anything: something interrupted it. Heat, power and hardware faults produce the second kind, and driver or system faults usually produce a blue screen or kernel panic first. Working out which kind you have narrows the search enormously before you touch anything.
Step by step
- Note whether it restarts cleanly or cuts out.A clean restart with a progress screen means the operating system chose to. An instant black screen and reboot, with no message, means power was lost or the hardware faulted. These lead to completely different causes.
- Look at when it happens.Overnight or when idle points at scheduled updates and maintenance. Under load — gaming, video calls, exporting, a big file copy — points at heat or the power supply. At a specific moment, such as plugging something in, points at that device.
- Read what the computer recorded.On Windows, open Event Viewer, go to Windows Logs then System, and look for a critical event at the time of the restart — Kernel-Power event 41 is the standard entry for an unexpected shutdown, and its detail sometimes names a cause. On a Mac, Console shows panic reports, and System Information lists recent shutdown causes.
- Rule out updates.On Windows, check Windows Update history and the active hours setting, which governs when it is allowed to restart. On a Mac, check whether automatic updates are set to install overnight. This accounts for a large share of "it restarted on its own" reports.
- Check temperature and airflow.A machine that shuts down under load and is hot to the touch is protecting itself. Blocked vents, a fan clogged with dust, a laptop used on a duvet, or dried-out thermal paste on an older machine all produce exactly this. The catalogue's guides on an overheating laptop and cleaning inside a computer cover the safe way to deal with it.
- Test the power side.On a desktop, a failing power supply causes instant restarts under load and is a common cause on machines more than a few years old. Try a different, known-good wall socket and avoid extension leads shared with heavy loads. On a laptop, try running on battery alone for a while — if it stops restarting, the charger or its connection is suspect.
- Disconnect everything you can.Unplug external drives, hubs, docks, printers and anything else, and run the machine bare for a day. A faulty USB device or a dock drawing too much can drop the whole machine, and this test costs nothing.
- Boot into safe mode and see if it stops.Safe mode loads a minimal set of drivers. If the restarts stop entirely in safe mode, the cause is software or a driver rather than hardware, and the next step is to work out what changed — a recent driver, a recent update, or a recently installed program.
- Check for a memory fault.Windows has a built-in memory diagnostic, and Macs have hardware diagnostics accessible at startup. Faulty memory produces random restarts and blue screens with varying error codes, which is otherwise a very confusing pattern.
Common mistakes
- Reinstalling the operating system first — It is hours of work and it fixes nothing if the cause is heat, power or memory. The event log takes two minutes and often names the answer.
- Assuming random restarts mean a virus — Malware that reboots a machine constantly is rare, because it defeats its own purpose. Heat, power and drivers account for the overwhelming majority.
If it doesn't work
Restarts at the same time every night
Cause: Scheduled updates or maintenance — Fix: Set active hours on Windows so it cannot restart while you use the machine, and check any scheduled tasks. This is the benign version of the symptom.
Restarts only during demanding tasks
Cause: Heat or power supply — Fix: Clean the vents and fans, check the machine is on a hard surface, and on a desktop consider the power supply. This is the pattern that most reliably points at hardware.
Blue screen or kernel panic before each restart
Cause: Driver or system-level fault — Fix: Note the error name shown on the screen. The catalogue's guide on blue screens and kernel panics covers reading it, and the name usually points at a specific driver.
Started right after installing something
Cause: New driver or software conflict — Fix: Uninstall it, or use system restore on Windows to go back to before the change. The catalogue's guide on undoing a change that broke a computer covers this.
Restarts on a laptop only when it is on charge
Cause: Charger, cable or socket fault — Fix: Try a different known-good charger of the correct specification. A charger that intermittently drops out looks exactly like a random restart.
Restarts when you move the laptop
Cause: A loose internal connection or a failing battery — Fix: This narrows it to hardware. A swollen battery in particular can flex the board — the catalogue covers swollen battery safety, and it is not something to leave.
Questions people ask
Is a computer that restarts itself damaging its files?
Each unexpected shutdown risks corrupting whatever was being written at that moment, and repeated ones eventually damage the file system. It is worth making sure your backups are current before spending days diagnosing.
How do I stop Windows restarting automatically after a crash?
In advanced system settings, under startup and recovery, there is an option to automatically restart on system failure. Turning it off means the blue screen stays on the screen long enough to read, which is genuinely useful for diagnosis.
Could it be the wall socket?
Occasionally, and it is worth ruling out because it is free. A shared extension lead with a heater or a laser printer on it, or an old socket with a poor connection, can dip the supply enough to drop a desktop.