Did you just add this drive from another system?
If so, then you need to become the owner of the drive and replace all the permissions of all files and folders.
I did just come across a trojan on a client's machine; he was surfing the net as Admin rather than the Power User account I set up for him; and this thing called it's self the hard drive cleaner. It went through and marked every file and folder as Read Only, System, and hidden.
Once I booted up in command prompt and killed/removed the trojan, I had to painfully attrib *.* -r -s -h /s all of his drives.
So even things that should be marked as system files and be hidden are now not. But the Trojan is gone and my client has all of his files back.