Kishore Kamal :
Try to reorient the two parts. Mine also two 4 pins for mobo power. It took 15 min to make it insert into motherboard 8 bin socket.
^ Don't do that. Its possible to insert the wrong cable if you do it backwards and fry stuff.
What cables you want to use are the 4+4pin, its also called an 8 pin but 4+4 refers to it being able to be split into two 4 pin connectors. There is also a 6+2 pin,
do not use this if you put it in backwards it will fry your board and almost positively your psu aswell.
Here is a picture of the connectors I am talking about
use the red one, not the blue one
If you like you can upload a picture of the connectors and we can tell you which one exactly.
Edit: Oh wait, I think I misinterpreted your first post. If you were asking about the lack of a 4+4pin + an additional 4 pin for the mobo then its fine. The extra 4 pin is for extremely high end overclocking. (talking cooled by liquid nitrogen here) Its not needed, only the 8 pin is needed.