are you attempting to delete OS a file? if so, you might have to take ownership of the file or directory first.
in cmd.exe as a admin
something like takeown.exe /f c:\pathtotheevilfileorordirectory
then give yourself full control rights
cacls.exe c:\pathtopathtotheevilfileorordirectory /G yourusername:F
then try to delete.
if that does not work try going to safe mode and try again.