I'd have to say that if you were having problems with the DVD drive and you are now having problems with the DVD drive then possibly the problem is with the drive. Do you have an old one lying about that you can try, or do you have access to another one? Could be worth trying an IDE one if you can get hold of one. In this country I can get a DVD drive for under £10 (less than $20), so it may be worth just buying another one.
You could also try making another bootable DVD, say of a Linux distro, and see if you get the same problem.