Hard drive

Hello!
i have problem in my Computer . I am using Windows 7.
The problem is that i don't know what type of threat came in my PC through net or external drive. it hides all my folders of only external hard drive. whenever I open the external hard drive i cant see any Folder (file are present there) but when i see properties of that drive it shows data. If i know the name of folder like my picture when i type it in address bar I:\my picture then it open n show my data. how to remove this prob?
what type of virus is this?I have tried to scan the external hard drive using Nod 32 Antivirus but i cant see them. plz help me if any body know this. (my external Drive is SP silicone power)