|Your analysis is wrong. Just because the fans turn doesn't mean the the PSU is good.|
Do you have all the required power connections to the graphics card and the auxillary CPU power made up?
Just your CPU and graphics card can pull almost 25A@ 12v. Your 12v rail is rated at 38A but that doesn't mean it is supplying that much.
Remove the graphics card after unplugging the computer and then try booting with the onboard GPU.
Disconnect any unnecessary external hardware too.