How do I turn my pc on just with the powersupply

Solution
There's an easier way for most people. The trick is to recognize that the "Reset" pushbutton on the front of your case is exactly the same type of switch as your On/Off button, and you usually do not use that button. So, inside your case, the several front panel controls plug into a multi-pin header on your mobo usually at the bottom right. Two wires (might be a pair, might be separate individual connectors) are labelled "PWR" and come from your broken On/Off button. Two other wires are labelled "RESET". Just disconnect the PWR set, and move the two from the RESET switch over to those header pins. Now you have no Reset button, but your front panel Reset switch will work as your On / Off pushbutton.

Paperdoc

Polypheme
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There's an easier way for most people. The trick is to recognize that the "Reset" pushbutton on the front of your case is exactly the same type of switch as your On/Off button, and you usually do not use that button. So, inside your case, the several front panel controls plug into a multi-pin header on your mobo usually at the bottom right. Two wires (might be a pair, might be separate individual connectors) are labelled "PWR" and come from your broken On/Off button. Two other wires are labelled "RESET". Just disconnect the PWR set, and move the two from the RESET switch over to those header pins. Now you have no Reset button, but your front panel Reset switch will work as your On / Off pushbutton.
 
Solution