Sims 4 not launching and says it’s running

Lily_2324​  Do you see the "already running" error message?  Or are you saying the game shows as open in the EA App or in the Task Manager but isn't on your screen?  The "already running" error has a master thread with troubleshooting steps here:

[CURRENT ISSUE] Sims 4 already running | EA Forums - 11818313

If you're not seeing the error, please let me know whether you have any mods or custom content installed, and if you do, remove them.  If that doesn't help, please provide a dxdiag.  Click Windows key-R, enter dxdiag in the run box, wait for the scan to finish, click "Save all information," and save the file to your desktop.  From there, you can attach it to a reply using the paper clip (Attachment) icon included with the other formatting buttons.