|Try this. Turn off the computer and remove the mains plug. If it's a laptop remove the main battery. Now hold the power off/on key in for at least 20 seconds. It probably won't help but there is "a chance" and it's quick to try.|
Does the drive show in BIOS? If not then either there is a problem with its connections or the drive itself has failed.
Here's another option:
Create a Linux Knoppix CD from here:
With this you should be able to see the contents of all HD's. If you can see your D drive with this then it proves that it is a Windows issue, rather than hardware.
In fact I use Puppy Linux Live CD but whichever you one you use the general instructions on that link are useful.
Always pop back and let us know the outcome - thanks