My Game Won’t Load

@maggie_p139  That's fine, I just didn't want you to end up running in circles if the answer was simple.  Since it's not simple though, you can try the suggestions near the end of this guide:

https://answers.ea.com/t5/Technical-Issues-PC/CURRENT-ISSUE-Sims-4-already-running/m-p/13276380

Most of the troubleshooting steps aren't relevent or you've done them already, but the two sections labeled "Reset permissions for Documents" and "Move/restore location of Documents" may be helpful.  Please try them, in that order, and let me know whether they help.

The alternative is to simply play in the new Windows account rather than your old one.  If you want to transfer your saves or other data, drop the files or folders into C:\Users\Public, which is accessible from any user account.  There's no harm in switching accounts, and if the guide linked above doesn't help, that's probably your only move anyway, so feel free to skip the extra troubleshooting if you're fine with using the new account.