Empty Recycle bin.
Ensure that Pagefile is not set to D.
Show hidden / system files (via folder properties), delete.
From a command prompt, run dir /S /A:HS from the root of D to view the files,
Then attrib -H -S *.* /S /D to remove hidden and system attributes, then del *.* /S /D.
Use with caution!
Alternatively, just reformat the drive!
SD