When you're looking at your Steam Library where all of your games are listed, right click on Skyrim and then select properties on the menu that pops-up. On the next menu, select the Local Files tab and then hit Verify Integrity of Game Cache... Let that run and then see if everything's working. If so, great -- the issue was the missing files. If the problem still persists, you should disable all of your mods, re-launch the game, and see if the issue is resolved then. If so, there was an issue / conflict with one of your mods. You can then go through your mod list and disable one at a time to find the specific culprit. Let me know if the above works or not.