Hi
I have to say that it would be normal for your CD-Rom drive to show up as D:\ so that may have changed during the installation.
That may be why you aren't seeing the D:\ drive now that you had before.
As trouble pointed out, you do have a D:\ drive, but it doesn't show anything in it.
You could try changing the drive letter of the drive listed as D:\ to F:\ and then it would let you change the drive letter of your CD-Rom to D:\.
If you right click in the empty space shown as Drive D:\ do you get a drop down menu with any options on it?
You would need that to change the drive letter, you do this be right clicking on the drive in Disk Management and selecting Change Drive Letter and Paths.
Click Change and it will give you a list...