I had a similar problem the other day when I was in my Vista installation (although it happened briefly in XP once too but corrected itself). In my case, in My Computer, it would show a disk icon and the name of the disk in the drive, but when you double-clicked on it it asked if you wanted to format a blank disk, and if you tried to Explore, it showed it being empty.
THis is what I did to correct it:
First, verify your drivers are up to date.
Second, go to Device Manager (right-click My Computer, it'll be there), and go under 'DVD/CD-ROM Drives'. Check and make sure Device Manager says the device is working properly.
If so, as it did in my case (but obviously it wasn't
lol), right-click on the drive that is giving you problems, click Disable, wait a minute or so, and right-click it again and click Enable. After this, see if the drive works now (Mine did instantly after re-enabling the drive). If not, try a reboot and try the drive again. If the above steps don't work, the drive could be broken.
Note: the above disable/enable trick sometimes works on other hardware too (I've used it with my network connection several times over the years). Hope this helps!