the single 6-Pin connector is PCI-Express power used mainly for video cards. Your PSU should have a 4-Pin ATX12V P4 connector just like your old 300w gateway or it may have the newer 8-Pin version (EPS) of it which should be able to split into two separate connectors and provide you with the same 4-Pin ATX12V P4 connector. As a general rule, if a power connector doesnt fit properly, never force it in and turn on your computer.
You are correct, there was a (EPS) 8 pin plug that I separated into two 4 pin plugs. Each having 2 yellow and 2 black wires. I used that as the plug on the motherboard and it is up and running.
Thanks for the reply.