Some video files you downloaded from the internet, may require
certain link files or scripts in C drive to play back or stream the
media from it's orginating web site/s.
If you have re-formatted your D drive, I'm afraid streaming data
and licenses (applicable to WMA files) will have been wiped clean,
and hence unable to play them.
If your slave drive partition were damaged or corrupted, your video
file or whatever stored in there, will have been converted into
folders bearing names in hexadecimal format, and properties of the
folders will indicate zero byte size.