So I just bought and installed a Seasonic x-850 yesterday, and for some reason when I try to turn on my PC it doesn't turn on. I now have to hit the power button on my PC, and then I have to hit the power button on the PSU to turn it off and then on. Did I plug something in wrong or is the PSU's fault?
Recheck connections on power supply and on motherboard make sure they are secure and locked. Also check the power switch connector from the case to the motherboard, it may have come lose while changing out the power supply.