Windows PC keeps restarting even at the login screen—how can I find the cause?

Check Event Viewer, especially Windows Logs > System, for errors immediately before each restart. Kernel-Power events can confirm that the machine lost power or reset unexpectedly, while nearby disk, WHEA, driver, or bugcheck errors may point to the underlying cause. Also check the contents of SrtTrail.txt from the recovery environment if you can access it.

This may be hardware rather than a normal login problem. Check CPU temperatures, make sure the cooler is firmly mounted, remove dust, and verify that all power and motherboard cables are seated. An overheating CPU, failing power supply, bad RAM, or another unstable component can reboot the computer even in Safe Mode.

Back up important files as soon as possible. Repeated restarts combined with failed recovery attempts can be caused by a failing SSD or damaged Windows files. Run the manufacturer’s drive diagnostic and memory test, then consider checking the drive’s health before attempting a repair install or clean Windows installation.

If the system remains stable long enough, disable automatic restart after a system failure so a blue-screen error can remain visible. You can also test with one RAM module at a time and disconnect unnecessary USB devices. If it still resets before Windows fully loads, focus on hardware, power, storage, and firmware rather than malware or ordinary startup drivers.