Pc help needed

[Mattfreakboy]

My pc wont start up again ive checked the power supply with an Antec ATX 12v power supply tester and its working fine whats the next step to finding the problem? How does one test he mobo etc without the pc being on?

 

[Mattfreakboy]

Does it do anything when you short the power-on pins or does it merely sit there?

how do you short the power on pins?