It would help if you had said what O/S was installed?
I hope someone comes up with a miracle answer...... Unless you have a spare HD with all the previous contents of c: and d: safely cocooned you will have to start again from scratch.
You will have changed the paths of everything that was on d: and windows has now no valid record of where everything is.
The dismal suggestion I have is to beg, borrow or buy another HD, install your o/s on that, and then copy from your original HD all the data you can find.
After that it is the gritty business of formatting the orginal to clear everything off and a complete re-install.