Hi WillOldham,
Thank you for reaching Microsoft Community. I understand how frustrating it is to have our device randomly restarts while in the middle of working on something on the device. Definitely, this not the experience we want you to have.
May I know which Windows edition and version is your Surface Laptop 3 running? To check, you may go to Windows Settings > System > About.
Which Surface Laptop 3 configuration do you have? Intel or AMD?
Whenever the device restarts by itself, are you prompted with an error message or code? If yes, may we know what is the error prompted?
Do you experience some lags or freezing also on the device before it restarts or it will be working fine then suddenly the device restarts turning the screen black?
For now, kindly try running these steps below on the device to make sure all drivers and software are up to date and no corrupted system files then observe if still the issue persist:
1: Run Surface Diagnostic Toolkit
See: Fix common Surface problems using the Surface Diagnostic Toolkit (microsoft.com)
2: Check for Windows Update
Go to Windows Settings > Update & Security and select Check for updates
Make sure all updates need are installed including Optional updates
3: Update drivers and firmware
Check what is the current OS Build of your Windows version by going to Settings > System > About.
Go to Download driver and firmware for Surface, choose Surface Laptop
Then click the link next to Surface Laptop 3 then click Download on the next page.
Choose the .msi file that matches your current OS Build and click Next.
After downloading, run and install the .msi then Restart.
4: Run System File Checker Tool and DISM commands
Open Command Prompt (Run as administrator)
Type and enter these commands below:
DISM /Online /Cleanup-Image /CheckHealthDISM /Online /Cleanup-Image /ScanHealthDISM /Online /Cleanup-Image /RestoreHealthSFC /scannow
Note: Allow each command to complete its process before entering the next command line
Exit Command Prompt and restart the Surface
If still issue persist after the steps above, please run the Windows Memory Diagnostic Tool on the device. To do this, press Windows key + R then type mdsched and click OK. On the pop up window, select Restart now and check for problems (recommended). The device will restart and start the diagnostic and it'll automatically boot you back to the desktop once the diagnostic is done. Once done, open the Event viewer and view the results under System log. Look for MemoryDiagnostics-Results.
Kindly check also in the Reliability Monitor what are those critical events that caused the random shutdowns on the device. Search for reliability in the Search menu of the Taskbar and select View reliability history (Control Panel) from the results. Once you have the Reliability Monitor window open, see if there are red x icons on the graph. If yes, select one of the red x icons then see below the graph for the Critical events sections. Double-click an item listed to view its details. If possible take a screenshot of the Reliability Monitor window and the details then share them with us here.
Kind regards,
Marrion