Can't play my game! Help! 0_0

I paid for the game (Digital Download) and all the updates and I was stupid and downloaded some mods(none that change the gameplay, just hair, clothes, flooring,wall covering and trees) and now my game won't start. I deleted some picture files that were packaged with the mods so it wouldn't cause a problem when I played, but it seems I deleted a file that was needed for the game to play.

It told me to re-install the game, but I can't figure out where to do that. Also, when I DO re-install it, can someone please tell me if I can put those mods back in without problems as long as I don't delete the added files that came in the packages? I'm not techie at all and am just trying to keep my old computer from dying under the weight of all I have downloaded and put on it. Oh, here's the error I got...maybe that will help.

Unable to start;

Cannot start because required game data is missing or damaged. Please try reinstalling the
game.

[85262c58:29f00e76:00000000:00000000]

Thanks in advance for any help. 🙂