Be careful that what you are trying to delete is not a system file.
Windows has special protection on the root of any drive, so you need administrator rights to create or modify files in the root of the drive.
Just being an admin user doesn't necessarily give you this because of UAC.
Right hand click the folder and select properties.
Click the security tab.
Click Advanced.
Click the owner tab.
Click edit
Select your user account
Tick "Replace owner on subcontainers and objects"
Click Apply
Click OK on each Window.
Now see if you can delete the folder.