I was playing the last part of the first dawnguard quest and my Xbox HDD CRASHED! Now I have to start over again! Not to mention ALL OF MY SAVE DATA FOR ALL MY GAMES ARE GONE! Thanks a lot Bethesda... Btw I had only been playing for about an hour so I know it didn't overheat!

If your HDD completely crashed, the game you were playing is completely irrevalent to the cause of the issue. Sounds more of a hardware issue if anything.

How old is your system/what kind is it?