The disk drive will also only show up on the left panel if a disc is inserted into it. If it is still not showing up after you insert a disc; you should go to computer management -> click storage -> disk management -> find you dvd rom and right click on it and choose "Change Device Letter and Pattern". Change it to a different letter and see if it shows.
If you make the "Menu bar" visable under "Layout", you can go to "Tools" - "Folder options" - "View" and then uncheck "Hide empty drives in the computer folder". Now it will show up there even when empty.