4 or 8 pin cpu connectors

[harold01]

i´m in doubt. i just got a p8z68 v gen3. when i installed the 8 pins (4+4 pin) of the psu into the cpu 8 pin connector everything started but 1 second later shut down and rebooted. when i placed only 4 out of the 8 pins it started as if nothing happened before, was ok. what´s going on? is it only 4 pin that i should install or what?

 

[mubin]

What psu do you have? Is it low watt psu?