Do what Fza asks and also check your MB header pins, you won't be the first person to pull the switch wire off, and failing that with the power disconnected jumper the power switch pins on the MB to make sure it's not the case switch itself that is broken, obviously re-connect the psu power to the wall to test, i.e make the wall plug switch into a temp on off button.
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DOING ANYTHING I HAVE SUGGESTED IS AT YOUR OWN RISK, NEITHER I NOR SEAGATE TAKE ANY RESPONSIBILITY, IT'S YOUR CHOICE TO DO WHAT YOU FEEL IS BEST FOR YOU
