You aren't trying to overclock it are you?
If you haven't done anything out of the ordinary to it you could try changing the parts with equivalent ones if you have them, sometimes you can get faulty equipment out of the box. Try checking for unnecessary hot part after you turn your computer on, might help you find out what the problem is.
To tell you the truth I would take it to the person who sold it to you and ask for their help. If that person still cant get anything to work then tell that person to refund your money and goto:
http://www.newegg.com
It may cost a little bit more then a used mobo/cpu, but you might not be able to get the mobo to work period. I have had trouble with the computers I have built and sometimes you can fix them and sometimes you cant. Take the easy route and buy NEW. Only my opinion though.
Good luck