Is there anything specific you have been storing on the D partition?
You can double click on one of the folders to see if there are more subfolders or files you might be able to idenitfy. Might drill down to the file level on one or two of these and post another screenshot.
Where do you store your programs?
Finally, these GUID folders are almost all done at 3AM, when you might be automatically backing up your C drive. Are you running Win-7 BackUp and Restore on a schedule at night, or some other scheduled process for that time?
That might give us an idea of whats stored here, and if it's safe to delete.
On this D drive, in the toolbar click on Tools, then Folder Options, then View. Click on the radiobutton that says Show all hidden files, and show hidden files folders etc.
That will show you all hidden files and folders on this drive. Also make the column visible that shows the file size of each of these entries.
Then give up another screenshot.
Another troubleshooting trick you can do is download and install on your C drive the applet called WinDirSTAT:
Here is the URL http://windirstat.info/
It's free. When doe you can just delete it if you don't need it anymore.
It will show you on this drive once everything is visible exactly what is taking up all the space.
One last thing to show is to go to Disk Management, especially the lower graphical area, upload a screenshot of the Disk Management dialog box, which will show if you have any ESP or MSR or other hidden partitions on this Drive0 Drive.