There are two things I can think of. The first does not really sound like your problem, but you might check.
In the Control Panel under Folder options, View tab, there is a setting to hide empty drives in the Computer folder. You might see if that is checked.
The other thing is you might check for a firmware update for the DVD drive. Mine was doing the same type of thing, like only showing up when the tray was opened and the firmware update solved the problem.