New Power Supply Not Working

[jroberts0113]

Hello,
I just put in a new 850 watt power supply. I connect every component, press the power button, everything starts spinning, but it doesn't boot. It just turns off. The old 300 watt supply I'm replacing still works, but it's not quite enough to run things right. Why isn't the new one staying in & booting?

 

[mcnumpty23]

have you connected the 4/8 pin connector ?