Check the card and how it is fitted in the slot.
The title says everything. I have an nVidia ASUS GTX 460 graphics card that was working fine before. Whenever I pop the CD in that came with it, the drivers won't install, and when I download them from the nVidia webpage, I try to install them and it says "Unable to detect graphics card." Everything's plugged in, considering I didn't unplug any cables through the reformat session. Any ideas?