|"The DVD drive just disappeared, cannot see or access it at all (I can still see my CD-ROM).|
I believe it's a registry problem, but I might be wrong."
I was expecting something about its status in the device manager but did not read that - how is it listed in there? (if at all)
If it is then it might be a Windows or driver issue, the advice about scanreg restore is a very good and easy one if you do recall when all this began. If that is not an option or the problem persists afterwards let us know.
At this time my advice is to go into real DOS via a boot diskette and see if the drive is accesible after changing directory to the optical (DVD) drive. If you are unable to read from it even from that environment, then something may be physically wrong with the drive or its connection in the case.