Well, tomorrow, I'm going to try the DVD drive in another machine and see if it will work. This thing has been driving me nuts, and I'm beginning to think that it may be a quirk of the drive itself, which would be truly odd, as it can handle CDs just fine.

I have seen several drives that will lose their ability to recognize DVD's. I have also heard of the other way around. Never understood it myself, but at least you know you're not the only one.

DVD drives have two lasers. One for cd and the other for DVD. Just as BluRay has an even smaller laser that reads smaller pits on that disk.

I also have a drive that wont read some commercial DVDs. It just makes a clunking sound when it is trying to mount it (but some DVDs work fine). Another drive I have seems to read everything except it has problems with some CD-RW.

Well, I feel silly. It turns out that the drive doesn't work in my Windows box either (where another one does, perfectly), so I'm going to assume at this point that it is a hardware failure. I'll be purchasing a new drive shortly, and I'm fairly certain that it will work quite nicely with the new drive.

Thanks to all of you for all your help.