It is definitley the DVD drive that is messing up. I had the exact same problem with my sammy.
Consider adjusting or replacing the laser, or like myself, mod a samsung sd-616T. It's not hard at all if you follow the instructions step by step, although basic soldering skills are required.
I do recommend replacing the drive though, those babys will read ANYTHING you throw at it. But hurry up, there's just a few left out in the market since they're discontinued.
Also, just in case you do it, you need to change the firmware of the DVD drive in your computer first to make it compatible, the version you need should be in the guides on the tutorial section.
Good luck mate.