I think this is a problem when your system is affected by some virus or spyware.
The simple solution that I found was mentioned below.
Open the registry editor. (type regedit in the run command)
go to LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\Advanced\Folder\Hidden\NOHIDDEN
and change value with this name “CheckedValue” to 1 and also “DefaultValue” to 1 .
if your problem is not solved then you must check your windows with anti virus settings.
Best anti virus is (nod32)