Do you use a "Windows Post Installation Program" (like WPI, WIHU or another) to install your softwares? If yes, does it an automatically Shutdown or Restart of your Windows? If yes, I think it's the cause... EDIT: I had this problem with WIHU. The default theme was Luna... And when WIHU restart my computer, the theme switches to Classic... Then I choose to restart my computer manually and all was OK!