Ok, I have an iMac (details in the description) with some DVD issue. Whenever I put a DVD in, it does nothing, makes a few ticking noises, and then spits it back out. I know I have a DVD compatible drive because, when trying to install something by CD, it said I have a drive compatible with DVD's and to use the DVD instead of the CD. Then when I put in the DVD, it did the same, just like always. Help?