The 1st obvious thing would be a protected password or encrypted file. In that case you need to find the password or key, or the owner.
If you have recently install your OS. It is posible some file are still identified under the old OS system ID. There is an option to take owneship of such files, Usualy by right click the file or folder.
Google " Take Ownership" for more info.
last option would a file type that the acess has been restricted to on your work station to prevent virus infections. Talk with your system administartor.