Need a new mobo

Just because the PSU has a connector does not mean it must be plugged in. The connector you are describing sounds like a PCIe connector which plugs into a graphics card. Here is a link which describes the various connectors for the PSU
http://www.playtool.com/pages/psuconnectors/connectors....
You should be fine with what you have
Hope it helps to clarify things

I plugged everything in except the one cable. The main board has a 4 pin ATX 12v socket. Thats what I'm getting at. The ATX power socket. The PSU only has the 8 pin power plugs.

Take your pick mate all solid some are of course better then others i listed decent budget boards and mid high end boards the best two listed are the ASUS P8Z77-V PRO and GIGABYTE GA-Z77X-UD5H mobo:ASUS P8Z77-V PRO LGA 1155 Intel Z77 HDMI SATA 6Gb/s USB 3.0 ATX Intel Motherboard
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

mobo:GIGABYTE GA-Z77X-UD3H LGA 1155 Intel Z77 HDMI SATA 6Gb/s USB 3.0 ATX Intel Motherboard
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

mobo:ASUS P8Z77-V LK LGA 1155 Intel Z77 HDMI SATA 6Gb/s USB 3.0 ATX Intel Motherboard with UEFI BIOS
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

mobo:ASUS P8Z77-V LGA 1155 Intel Z77 HDMI SATA 6Gb/s USB 3.0 ATX Intel Motherboard
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

mobo:GIGABYTE GA-Z77X-UD5H LGA 1155 Intel Z77 HDMI SATA 6Gb/s USB 3.0 ATX Intel Motherboard
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

mobo:ASRock Z77 Extreme6 LGA 1155 Intel Z77 HDMI SATA 6Gb/s USB 3.0 ATX Intel Motherboard
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

Facepalm do you need a intel or amd motherboard

Simply use the 8 pin ATX on the 4 pin ATX, it'll overhang nothingness a little but it'll work just fine.

+1 it's worth a shot before spending money on a new mobo