Processor or Motherboard?

Hello

I was wondering if I could get everyone's opinion on my problem..Im fairly sure it is my processor, but I really wanna know before spending money. Any ideas will be appreciated.

I recently bought this motherboard JetWay 775GT1-LOGE LGA 775 Which was suppose to be used with a pretty old(3 years old) Prescott Pentium4 3Ghz processor, and everything worked fine for about a month. One night I turned off the computer as I regularly did and the next day it decided not to work anymore. When I try to push the switch it would attempt to turn on but it just 'dies' right away(meaning the power on led would flash and the ps would try to start but wouldn't). I already tried different power supply and during that process I noticed that if I didn't plug in the 12v connector on the mb the PS would start working normally, but if I plugged it in, it would again try to start and die right away. When I removed the processor and connected the 12v connector, the PS would work normal.`

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