Dell Optiplex GX280 and PCI Express

[iamjn]

So I have a new Dell GX280 PC. The onboard video is the typical crap, so I want to upgrade it with this Asus n5900 PCI Express card. However, after I install the card, a message is received at POST:

"Alert! PCI Express card is operating in x1 mode."

The drivers install ok in XP, but the status page does confirm that it is not operating in x16 mode.
I have checked Dell's site, ASUS's site, and googled the problem, with no solution. Any ideas? I can't find any settings in the bios or on either board.

I've seen the members here solve some odd problems, so I am hoping someone has seen something similar.

thanks in advance!
iamjn

 

[mechBgon]

You have strange taste in gaming computers Anyway, let's start with power issues. I see there are three chassis styles and presumably you have the largest one, which has 305W and 250W power-supply options. Which one's yours equipped with (look at the label on the side of the PSU) and do you have the auxiliary power cable hooked up to your video card to supply it with the necessary power?

 

[iamjn]

The PSU is the 305w one. With the PCX5900, there is no aux power connectors needed.