Completely Broken Game

@meadowings044406  Since you own Sims 4 through Steam, you'll need to repair through Steam.  Open your Steam library, right-click the Sims 4 tile, and select Properties > Local files > Verify integrity of the game files.

If that doesn't help, please test in a clean user folder.  Move the entire Sims 4 folder out of Documents > Electronic Arts and onto your desktop, and when you launch the game, a clean folder will spawn with no content.  (Your saves and other content will be intact in the folder you moved but temporarily not read by the game.)  Don't add anything to the new folder yet; just start a new save and let me know whether everything is back to normal.

The computer shutdowns are also concerning and should be addressed as soon as possible.  For that, let's start with a dxdiag.

https://help.ea.com/en-us/help/pc/how-to-gather-dxdiag-information/

Repairing it through Steam fixed the broken CAS, thank you! But as soon as I load into gameplay; my whole computer shuts off again. I tried testing in a clean user folder like you suggested but again, as soon as the game unpaused in live mode, my computer shut off and on ☹️ I attached the dxdiag! Thank you so much for your help!!

@meadowings044406  Your dxdiag contains a few generic Windows errors, but nothing that would explain a shutdown.  So I'd like to see the results of some hardware monitoring.  Please download hwinfo (it's free) from here:

https://www.hwinfo.com/download/

You don't need to install anything; just choose the Portable version, unzip it, and launch it from Downloads or wherever you like.  If you do want the full installer, be sure to click the button for hwinfo itself, not for lansweeper.

Restart your computer, open hwinfo, choose Sensors Only, and click the button that's a sheet of paper with a + to start logging.  Save the log file to your desktop for easy access.  Wait five minutes, then open Sims 4 and mess around in CAS for at least 10 minutes, then go to live mode.  Don't alt-tab out of the game or run any other programs, aside from the EA App of course, while you're testing.  Even if your computer shuts down, the log should be intact up until that point, but please keep track of how long you were logging so I can check that against the time span of the file.

Please upload the log to the third-party filesharing site of your choice (Google Drive, Dropbox, etc.) and link it for me.  Either leave it in .csv format or, if you're going to use OneDrive, create a .zip file, and don't open the log before uploading it, or else my log reader might not be able to interpret it.

Please also let me know the specs of the power supply in this computer.  I'd like the model, wattage, and rating, for example Corsair 750W 80+ Gold.  You can see this info on the unit itself, which, in case you're not already aware, is the box into which you plug the power cord.  You'll probably need to remove a side panel to see the info, but that's all.