I installed a XFX nforce 780i 3-way SLI Motherboard with a intel core 2 Duo E8400 Processor 3.0 GHz.
when I power up the machine, nothing happens except for a blue light on the motherboard lights up. The power supply does not come on at all, no fan or anything except for the blue light on the motherboard Can anyone tell me what the problem maybe ? I am taking the power supply back to where I bought it. I suspect that it has a problem.

Is it a new build or have you had it working before?

it is a new motherboard and power replacement.

That didn't answer my question. Have you had it working before?