Sims 3, need help uninstalling?

I need to uninstall the game, because the launcher won't open and I'm pretty sure it's because of corrupted custom content. When I try to uninstall it, it says that I can't because it's running, but it's not. I tried restarting my computer, but it still says it's running. How do I get it to stop running so I can uninstall it?