The first information that would help us focus down on the problem is where it is missing.
Is the D a second drive or a partition on the C drive? If you don't know, how many physical drives are on your system?
If it's a second drive, can it be detected in the Device Manager? If you open Disk Manager, does it show up in the pictures of stripes on the bottom or not? If it does, what does it say on the stripe?
And checking connections is always a good first step, rolli59