I was simply playing Dawnguard. I had just finished the entire Dawnguard questline when I saved and got off for about 2 hours. When I got back on, I tried to load my last saved game but it said something like 'saved game is corrupted'. I have already deleted the DLC and redownloaded, but it still won't work.
As the message says: "saved game is corrupted" (it's not a DLC problem). You should start from another save point previous to that one because everything that you save after that (if you can save anything at all) will still be corrupted in a way or another. Always keep several save points in any game, specially Bethesda games (mainly Fallout series). If you have no previous save point I'm afraid to say that you will have to begin a new campaign.