Have you reinstalled Skyrim?
From Mark41:
Do a clean install that way:
First do a standard uninstall. (Control Panel\All Control Panel Items\Programs and Features-> Uninstall The Elder Scrolls V: Skyrim)
Next, delete your skyrim folder under C:\Program Files (x86)\Steam\SteamApps\common\
Backup the Saves folder first, then delete your Skyrim directory under Documents/ My Games (saves folder is there)
Then under C:\Users\[Your Username]\AppData\Local\ - Delete the Skyrim folder that is in it.
(You should enable to see the hidden files under windows to delete that folder.) HOW: (View - Options - Folder Options - View - Advanced Settings: Show hidden files, folders and drives)
I recommend you make a system restore point before you run ccleaner. http://windows.microsoft.com/en-us/windows7/create-a-restore-point
Use Ccleaner after all this (http://www.filehippo.com/download_ccleaner), and install your game again, from scratch. !!!!
You don't need to uninstall Steam.