Hi there,
are you sure that the switches on the PC case are working correctly?
Have you added any new hardware to your system recently?
Could you post back with your full system Spec's so we know what hardware you're running?
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      Operating System
         MS Windows 7 Ultimate 32-bit SP1
      CPU
         Intel Core i3 530  @ 2.93GHz   38 °C
         Clarkdale 32nm Technology
      RAM
         4.00 GB Dual-Channel DDR3 @ 666MHz (9-9-9-24)
      Motherboard
         Gigabyte Technology Co., Ltd. H55M-S2 (Socket 1156)   25 °C
      Graphics
         SMB2030 (1600x900@60Hz)
         Intel(R) HD Graphics
      Hard Drives
         488GB Seagate ST3500418AS ATA Device (SATA)   32 °C
      Optical Drives
         HP DVD Writer 1260r ATA Device
      Audio
         Realtek High Definition Audio
Full details can be found in the attached 
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I think the switches are working since I can switch it off manually pressing the power button for few seconds. I have not added any new hardware .