Re: [CURRENT ISSUE] Sims 4 Unable to Start, Already Running

@VioletFirehock  Thanks for the dxdiag, which shows some generic Windows update errors but nothing that explains why Sims 4 isn't launching.  The fact that the game works in the new user account suggests that the problem is with the Sims 4 user folder in your current account.  This can have several causes, one of which is OneDrive blocking access to the folder.  So please try pausing syncing while you play; right-click the cloud icon in the lower-right corner of your screen to see the option.

If that doesn't help, please drag the entire Sims 4 folder out of Documents > Electronic Arts and onto your desktop.  If it copies rather than moving, or you get an error when trying to move it, stop here and let me know.  Otherwise, try to launch the game.  If it works, a new 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 let me know whether you can get far enough to start a new save and play in live mode for a bit.

If that doesn't help either, please let me know whether you've ever used a different antivirus on this computer.

@swalsh0794  Please try the above as well, and I'd also like to see a dxdiag if the above doesn't help.

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