Video Card / PCI Express problems?

i bought a secondhand Alienware Area-51 Desktop from craigslist about a year ago, I don know the exact model but I know the owner of the computer bought it in 2007 but has upgraded it since so it is somewhat old, but runs some of the non-graphically intensive games very good. The graphics card this computer has is a GeForce 7900 GT/GTO and i have been looking to upgrade it ever since.



i bought a new card and while installing it i noticed my current card has a blue, 6-pin cable attached to it labeled as "PCI Express 2.0", not sure what it does, but the new card did not have an input for this cable, so i assumed it was optional or not important and just left it. although now while playing with my new card; it would overheat, and i assumed it had something to do with the cable that wasn't attached.



So i returned that card and bought a XFX Radeon HD 4670. but it turns out that this card doesn't have an input for a "PCI Express' cable either, although on the box under the key features i noticed "-PCI Express 2.0 support".



So wtf? I can't find the input for this cable and i am afraid to install it because i think it will overheat again just like the other one. Can someone tell me what to do? tell me what is the purpose of this cable, and why both of the new cards i have bought don't seem to have an input for it?



the "PCI Express" cable inside my computer that is plugged into my card i am talking about looks just like this.

http://www.playtool.com/pages/psuconnect…

on the left being the end that plugs into the card.|||This 6 pins connector is a separate power supply for the newer PCI Express video card. Not all PCI Express video cards are using this. If the video card that you buy doesn't have this kind of input, don't worry, just make sure it has a fan and working to avoid overheating.|||That's the power cable for the graphics card. Lower end cards, like the 4670, can draw enough power from the PCI-e slot, and don't need the power cable.

If your power supply is rated for it, you should go for something in the upper 5000 series.