When I see that I pull out my USB DVDRW drive to try the media on my drive. These drives can get dust on the lens as well as work or not work on all media. There's a reason I keep an USB DVDRW around.
I have three operable Apple computers. I also have an instructional DVD pertaining to another electronic device. The DVD will mount, automatically launch DVDPlayer, and play as I expect it to on my wife's iMac and on my old laptop. But it will not mount on my iMac. After loading, my iMac sits for a while then ejects the DVD with no activity and no explanation. Another commercial (movie) DVD does mount, launches DVDPlayer and seems to work fine on my iMac. Also, the Apple DVDs for System and Other software mount and automatically start DVDPlayer. (Both iMacs are Intel machines running OS 10.6.8 Snow Leopard.) So what is the problem? The DVD itself? My pre-installed version of DVDPlayer? And what is a remedy?