First Open Steam and go to Library. Select the game and click the gear icon. Open Properties. Select the Local Files > Verify Intergrity of Game Files… In this way, you will ensure that the files are verified and the corrupted ones are downloaded again. Enjoy!

I installed mods for the game I installed from Steam and the game is broken

First Open Steam and go to Library. Select the game and click the gear icon. Open Properties.
Select the Local Files > Verify Intergrity of Game Files…

In this way, you will ensure that the files are verified and the corrupted ones are downloaded again.
Enjoy!