Old thread, but this was bugging me. This is Win 7 pro 64.
Half of my computers show the DVD drive even when there is no disc in the drive (in win explorer / file mgr), but the other half wouldn't. Put a disc in and it shows up as E:. Take the disc out and bye bye. These were ALL machines restored from the SAME backup onto very similar ThinkPad T61s. It drives me crazy because when I put in a USB, it will grab the E: drive letter that is supposed to be for the DVD drive. I have backup / sync routines that want the USB sticks to be G: or H:. These machines usually have internal or local attached drives C, D, E, and F already in use and the USBs are G and H.
I found the setting. It's in Win explorer.
Tools / Folder Options. General Tab.
Make sure the box that says Show All Folders it checked and the empty DVD drive now shows up!