The steps are :-
Open registry( select run command from start menu and type regedit and then press enter)
In the left pane goto path HKEY_LOCAL_MACHINESoftware\Microsoft \Windows \CurrentVersion \Explorer \Advanced \Folder \Hidden \SHOWALL
Delete the value CheckedValue in the Right pane by right clicking it and selecting delete. (Its type should be REG_SZ and data should be 2.)
Create a new DWORD value called CheckedValue by right clicking in the Right pane and then selecting new -> DWORD Value and then changing the name to CheckedValue. (same as above, except that the type is REG_DWORD). Modify the value data to 1 (0×00000001) by right clicking the CheckedValue in the Right pane and selecting modify and changing the value data to 1.
This should let you change the “Hidden Files and Folders” option.