Windows 11 quick way to check when a computer was restarted

check its "uptime" in the Task Manager, which displays how long it's been running since the last boot. For a detailed log of all restarts, you can use the Event Viewer to find the last boot time or a specific restart event ID. 

1. Right-click the taskbar and select Task Manager, or press Ctrl + Shift + Esc.
2. Click the Performance tab.
3. Select CPU on the left pane to view the system uptime in the bottom-right corner.
4. The uptime is displayed as Days:Hours:Minutes:Seconds. 

1. Open Command Prompt by searching for "cmd" in the Start Menu.
2. Type systeminfo | find "Boot Time" and press Enter.
3. The date and time of the last boot will be displayed

Method 3: Event Viewer (detailed log)

1. Open the Run dialog by pressing the Windows key + R.
2. Type eventvwr.msc and press Enter to open Event Viewer.
3. In the left pane, navigate to Windows Logs > System.
4. In the right pane, click Filter Current Log.
5. In the "Includes/Excludes Event IDs" box, type 1074 to see recent shutdowns and restarts. You can also look for Event ID 6005 (system start) or 6006 (system shutdown).
6. Click OK to view the filtered log.