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

kcc0rauniio4​  With the new account, there shouldn't be anything missing on the user files side.  For the game install side, you can do a clean uninstall of Sims 4 and the EA App, as described in the accepted solution of this thread:

[CURRENT ISSUE] Sims 4 DLC shows as installed, won't load in-game | EA Forums - 11831673

Then reinstall the game into a different, newly-generated folder, as described.

If this still doesn't help, I remember an issue with missing registry entries that also caused either this error or a related one.  I'll dig up the thread if necessary.  But a reinstall should create the entries.

If you'd like to be thorough before reinstalling the game, please run a couple of basic checks of your Windows system files, which could repair some registry-related issues:

• Hit Windows key-X
• Choose either “PowerShell (Administrator)” or “Windows Terminal (Administrator),” whichever option is offered
• Inside the window that appears, copy and paste “DISM.exe /Online /Cleanup-image /Restorehealth” without quotes, and enter
• The system will start validating soon. If it throws an error, please list it here
• After it reaches 100%, hit Windows key-X again
• Again, choose “PowerShell (Administrator)” or “Windows Terminal (Administrator)”
• Inside the window, copy and paste “sfc /scannow” without quotes, and enter
• Post the message you receive here

Restart your computer, hit Windows key-i, select Update & Security, and click the box to check for updates.  If any install, restart again afterwards.