Please share more information like premiere pro version, OS version..any error you get before sudden shutdown. It seems to be the PC issue instead of Premiere pro maybe with the graphics card, RAM, or something else.
Vishu Aggarwal Adobe Certified Instructor, Professional and Expert
If that doesn't work, try resetting the Workspaces: Reset a workspace Reset the current workspace to return to its original, saved layout of panels. 1. Do one of the following: • Click the Workspace menu icon and select Reset to Saved Layout. • Choose Window > Workspace > Reset to Saved Layout. from here: https://helpx.adobe.com/premiere-pro/using/workspaces.html
If that doesn't work, try Preferences > Audio Hardware and set Input to None.
If that doesn’t work, try updating or rolling back your graphics driver directly from the video card manufacturer’s site. If NVIDIA, do a clean installation of the latest Studio Driver (NOT the Game Driver)
If that doesn't work, try creating a new project and import the old one into it.
It sound like a classic over heating issue. If you start to export or pre-render the CPU, GPU and RAM will work hard, especially the CPU. When those part get´s to hot they simply shut down to prevent the parts to be destroyed by the heat.
And, a good tool to find out why the computer shuts down is the Event Viewer in Windows. Open Event Viewer, twirl down Windows Logs and click on System. That will reveal details. If you know when the computer shuts down it is easier to find. If the computer shuts down 2022-01-31 20:34:20 it is easier to find the posts around that time.