System won't boot with 8 pin connected but will with 4 pin

Hello,
I just completed a new build using the following:
ASROCK 970 EXTREME 4 AM3 ATX Mobo
AMD PHENOM II X6 1045T AM3 CPU
GIGABYTE **HD6450 1GB D3 PCIE DVH Graphics Card
CRUCIAL 8GB 4X2 D3 1600 DIMM CL9 Memory
ANTEC EA500D ATX PSU

The PSU has a 6+2 connector for the 8 pin CPU supply. When that is connected, I get nothing when trying to boot. If I remove it and use one of the 4 pins in that same connector (using the 4 sockets that weren't covered) the system boots and runs fine. With this CPU, it doesn't appear I need the 8 pin supply but I'm still trying to figure out what is going on.

Thanks,