Make HD 2600 AGP video card work on my OLD computer

I bought the HD 2600 AGP card last week.
I tried many time to install it on my old computer. All failed. I can not even make the PC boot.
Later, I found one six pin socket on the end of video card. I don’t know what it is and I can not find any explaination on the user menaul.
I google it and knows that the 6 pin socket is a power socket to give more power to Video card.
The problem is my PSU is old style without 6 pin plug.

Finally I got the cable from a small computer store.

When I installed HD 2600, connected two 4 pin regular power plugs and six pin socket of Video card by this 4pin-6pin converter cable, it works.
The video card is great.
Now my computer can play High-definition video and support more 3D features of Games.