I had the same issue. If you don't really care about your save files this could help because at least you'd get to play again. First of all, (if you are using origin) locate the file i.e. go to origin, click on sims3 and then click on "manage" then "view properties". "Open Folder" to the install location. If it opens to a C: location, check what folders are available. If this location seems to be lacking folders or seems to just have EP0# folders with no Saves folder or other, check your Microsoft OneDrive and look for the Electronic Arts folder and locate the sims 3 folder inside. If this folder contains a saves folder and/or others that were missing from the C: location; copy paste it from the OneDrive location to the C: location and then permanently delete the files from OneDrive (make sure to have a backup on a flashdrive just in case). Start the game to check.
IF the "Open Folder" takes you directly to OneDrive, (make a backup of the files on a flashdrive) permanently delete the Electronic Arts folder then start the game.
My save file had Dragon Valley content that disappeared after I did this so I think EA did something to their file confogurations. I'm not sure.
I'm still trying to figure out what went wrong but at least I can start a new game.
Edit: I went to install all the extra content from the website and it stopped working again.
I tried that but I don't think there is supposed to be save files in this location. The save files are in documents, the actual install of the game is on the :C Drive. I also put my documents directory back in its original location since moving it did nothing.
This is what's in my onedrive from what I can see. Nothing Sims 3 related.
