PC bought and built, but OS does not see Graphics card.

[laserspeeddemon]

Long story, short. I built and computer and I obviously suck at it. Cause it's not working the way I thought it would.

The problem. OS does not see the Graphics card.

OS: Windows 7 Professional x64
Motherboard: ASUS M3N-HD/HDMI
Processor: AMD Phenom II X4 920
Memory: Kingston HyperX Dual Channel 2048MB 1066MHz (x2 or 4GB total)
Graphics Card: HIS Radeon HD 6870 IceQ X Turbo
Power Supply: Aspire 600W DarkSide Alum Black PSU

Two things to mention.
1) The Mobo was sold to me second hand, but I was told it was NEW. (which is a lie because he left the processor in the Mobo).
2) The Mobo supports PCI Express x16 (PCI Express 2.0). The video graphics card is PCI Express x16 (PCI Express 2.1). Is this the problem?

 

[linkin]

PCI-E is all backwards compatible. So the 2.1 card won't be a problem in a 2.0 slot.

Make sure the card is in the first PCI-E x16 slot and has all the power cables in it. Then download the latest video drivers from www.amd.com

 

[laserspeeddemon]

PCI-E is all backwards compatible. So the 2.1 card won't be a problem in a 2.0 slot.

Make sure the card is in the first PCI-E x16 slot and has all the power cables in it. Then download the latest video drivers from www.amd.com

I put it in both (1st one which is blue and the 2nd one which is black).Doesnt' work on either side. The card has two 6-pin power connectors on it and I have them both plugged into the power supply. The graphics card fans come on FULL blast. And I have downloaded the driver "package" From both the www.HISdigital.com site and the AMD site.

To no avail. When I look into the display adapters (in device manager), I still see only the NVIDIA nForce 750a SLI (which I assume is the on-board video processor).