Mine had a problem similar to yours vampy.
It was also on autosave. The game would save the first case, but after I finished the second one, it wouldn't save anything after that.
After re-doing Speed's case about 20 times I finally realized that if I ever wanted to play the others I couldn't turn the game off. So I just blocked out like 3 hours of my day and did nothing but solve the cases one after another.
No one has any idea why it did this. I figured it was just the hazards of buying it at a yard sale...