CrashWhy

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Why did my computer restart overnight?

Published

RestartsWindows UpdateEvent Viewer

Most overnight restarts are Windows Update finishing an install outside your active hours. If it was not an update, Windows logged either a blue screen or a power loss — and the System log tells you which one.

The three usual causes

What you find in the System logWhat it means
Event 1074 (source User32) just before the restartA program or a person asked for the restart. The event names the process and the reason. Windows Update restarts show up here.
Event 1001 (BugCheck) and Event 41 with a non-zero BugcheckCodeA blue screen (Stop error). Windows restarts automatically after one by default, so you may never see the blue screen.
Event 41 with BugcheckCode 0, plus Event 6008The PC lost power or froze hard and could not write an error code — power supply, a power cut, heat or other hardware.

Check it in Event Viewer

  1. Press Win + R, type eventvwr.msc and press Enter.
  2. Open Windows Logs → System.
  3. Select Filter Current Log… and type 1074,1001,41,6008 in the event ID box.
  4. Find the restart time and read the events right before it. Event 1074 shows the process name and the reason; Event 41 shows BugcheckCode and PowerButtonTimestamp on its Details tab.

If it was Windows Update

Windows schedules automatic restarts after updates outside your active hours — the hours you normally use the PC. Microsoft's documentation gives the default active hours as 8 AM to 5 PM, so a PC left on overnight is exactly where an update restart lands. You can change active hours in Settings → Windows Update → Advanced options, or pick a restart time yourself when Windows asks.

If it was a blue screen

Event 41 stores the bug check code in decimal. Convert it to hexadecimal (Calculator → Programmer: 159 becomes 0x9F) and look it up in Microsoft's Bug Check Code Reference. The code points to the area to check first, often a driver.

If it was a power loss

When BugcheckCode and PowerButtonTimestamp are both 0, Windows had no chance to write a code. Microsoft's checklist for this case: turn off overclocking, test the memory, make sure the power supply has enough wattage, and check temperatures. A power cut during the night looks the same — a UPS (battery backup) prevents it.

Can I stop Windows from restarting by itself overnight?

You can move when it happens. Set active hours to cover the time the PC is in use, or schedule the restart from the update notification. Windows still restarts eventually to finish installing updates.

Why is there no blue screen if the PC crashed?

Windows restarts automatically after a Stop error by default. To see the code on screen next time, clear "Automatically restart" under System Properties → Advanced → Startup and Recovery → Settings.

Sources

Official documentation, checked 2026-10-16.

CrashWhy reads these Windows logs for you and explains what happened in plain English — free for Windows.