Fun (... if it runs for times)

I bought the game last week and am reasonably happy with it. I still have not played it, and also the multiplayer or co-op, I have not tried yet.
As already mentioned in the headline, I enjoy the game thoroughly, if it's not just crashes. This happens to me namely often (about 5 to 30 minutes between two crashes), so I constantly have to repeat sections of the story or even entire side missions. A mission I have already a more than a dozen times ranging from the front because the game my progress within the Mission does not store (although I will after I die back to the beginning, but once the game is crashing off the memory status and I have the mission to start over).
On the performance of my computer that can not lie, anyway. The is namely an Intel Core i5 3570K, 16GB RAM and a Radeon HD 7970th I play in 1920x1200 with maximum details.
Should anyone know a way to fix this problem so I would be very grateful to him for comment.