How do I get Skyrim to redownload Dawnguard and the other DLC if I accidentally deleted it from the data files menu?
- Load Steam
- From the Library section, right-click on the game and select Properties from the menu.
- Select the Local files tab and click the Verify integrity of game cache... button.
Steam will verify the game's files - this process may take several minutes.
If steam finds that files are missing from the game's directory, it should automatically begin to re-download them. This method has worked for users who are missing DLC [source]