If you enable "Show hidden files and folders" in the Windows Explorer, but still can't see any hidden files and folders and the corresponding checkbox in the folder properties is still unchecked, this is probably caused by a virus. To show hidden files and folders

1. Click Start -> Run -> type regedit -> hit Enter
2. In Regedit find
   
   Code:

   HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\Advanced\Folder\Hidden\SHOWALL

   Find the "CheckedValue" parameter and delete it.
   Create a DWORD parameter and rename it to "CheckedValue". Set its value to 1.
3. Open any folder. Go to Tools -> Folder options -> View -> Check the "Show hidden files and folders" checkbox.