Okay, this is a bit frustrating for me. For the past year or so I've been playing Sims 3 perfectly fine. However, at the end of July I stopped playing to play the Sims 2 Ultimate Edition. When I tried to go back to my Sims 3 game today I instead got an error message saying "Unable to start. Please reinstall the base game." This confused me, as my computer says the base game and all expansions are installed just fine. I tried going into the program files and skipping the launcher by opening the game manually, got the same error message. I honestly cannot tell what's wrong, as I haven't changed anything about my Sims 3 game files. I read somewhere else that performing a "factory reset" may fix my game, however I am unable to perform this factory reset as it assumes that I am able to run my game in the first place. Does anyone know what's going on? Much thanks to anyone who helps.