Can’t pwr Up!

Help! I have a gigabyte ga-71xe mobo(Slot A) with AMD Athlon 700 cpu that will not pwr up. I’ve change the pwr supply. The PC will pwr up when the CPU is not in the slot but when I put it back in, there is not pwr going to the system. I bought a newCPU and the same thing happens. I figure that the mobo is bad or the CPU slot is bad. Am I on the right track and what should I do next?
thanks for the help!