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As I expected , the USB drive was virused . To cure it , i did the following :
1- Scanned it with AVG , to remove the virus.
2- Opened the CMD as an administrator.
3- Entered the following command :
attrib -S -H /S /D
-S : Removes the system attributes.
-H : Removes the Hidden attributes
/S : Works on sub-folders and files.
/D : Works on the directories' attributes as well.
That's it .. Good Luck