It may happen that the option to display hidden files and folder is disabled or is not working. You can try either one of the following tricks to fix this problem:
Click Start, then click Run and type regedit
Navigate to folder HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\Advanced\Folder\Hidden\SHOWALL
Double click the key CheckedValue and enter the value 1
Close the registry editor.
Click Start, then click Run and type cmd
Type regsvr32 /i browseui.dll and press OK in the confirmation windows
Type regsvr32 /i shell32.dll and press OK in the confirmation windows