PC shuts down after only 3 seconds

[Rainydayown]

Hello this i the problem i have been dealing with and have been trying to fix for last couple of days and i hope that someone can help ne
My friend basically gave me his whole old computer and he helped me put it together. We forgot to plug in the audio cable i couldn't find were to plug it in at.
This is what happened i accidentally plugged what i know now is a plug from the power supply that is supposed to power a fan, well i accidentally plugged that into the motherboard were a usb slot or something is supposed to go and i forgot to unplug it from the wall so whenever i turn on my computer is basically turns on for 3 seconds and turns off, the only way i can turn it on is by plugging it in to the wall because now my power button doesn't work.
I have no idea were to begin
this is the computer gateway gt5034 (just google that because i cant post links)
Thanks

 

[Tmagic650]

Did you smell or see any smoke? We all made mistakes like this at the start... The motherboard is probably fried

 

[Rainydayown]

Yes dang it i did smell smoke, does anyone wanna point me in the right direction of were to find a replacement for this motherboard?

 

[Tmagic650]

Does this look like your motherboard:
Gateway Motherboard

 

[Rainydayown]

Yes, it looks like that exactly.