Can't even start MSFS on Steam any more?

Sometimes reinstalling the whole computer “might” help, since it clears up all the junk files that may have caused it. If the root cause is outside of the MSFS, then uninstalling and reinstalling the entire MSFS won’t help. At least by clearing up the entire PC and fresh install windows and then MSFS, you can eliminate the possibility of OS or MSFS and may look to hardware or driver issues.