Motherboard or psu?

[grinzz]

hi guys i have a problem with my pc after having to restart my pc quite a few times i returned too my pc and now i have no power at all.

Ive pulled the 24pin out f the mobo and shorted it with a paperclip and it starts up fine.

I reattached it too the motherboard andtried to short it with a screwdrver on the pwr switch pins and it wont start up.

Does this mean the mobo is screwed?

 

[grinzz]

e8400
p5q pro
4870 crossfire
toughpower 850w

Pulled everything out except mobo andone stick of ram. When shorted out with a paperclip the psu starts up the pump, fans etcs.

I just want to know which component needs to be replaced mobo or psu or cpu (not convinced its cpu but i could be wrong)

 

[jsc]

Our standard checklist and troubleshooting thread:
http://www.tomshardware.com/forum/261145-31-read-posting-boot-problems