Just a few suggestions - easiest one is to verify your game files. Something might be corrupt.

Make sure the game is in your anti-virus and firewall exceptions lists.

For the rest, back up your saves. There are loads of posts and info on the internet to explain how, before trying these other options.

Turn off Steam cloud saves, and try to load the game again.

If you are running mods - disable or remove them and try again.

Try a fresh re-install if none of that works.