Unable to start or uninstall Sims4

@lina_wxs  Try using Revo Uninstaller (the free version is fine) to remove Sims 4.  Before doing so, rename the Sims 4 folder inside Documents > Electronic Arts to something that doesn't include "Sims 4" in the name so Revo doesn't flag it for deletion.  Uninstall the EA App with Revo as well, for good measure.

If Revo can't "see" Sims 4 at all, then the alternative is to manually delete the folder that contains the game's program files, and use Piriform's CCleaner (the free version is also fine) to delete the associated registry entries and other hidden files.

If this doesn't help, or you want to try something else before you go through the trouble of reinstalling the game, the steps in the first post of this thread, which is for a related but distinct error, may be useful:

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