I was able to get my new VisionTek Radeon HD 7850 video card to work fine on another Windows 7 machine, so I'm really stumped.
On both computers, I went through the same process. Disable and remove the driver for my original video card. Install the 7850 and then download the AMD automatic driver detect program. Download the indicated driver, and run the install program. On my problem computer (specs below) the Catalyst program installs everything fine except for the driver. I get the error message, "Driver Install: Windows® version does not support this operation." I have no clue how to fix this and neither does VisionTek.
OS: Windows 7 Premium Home Version, 64 bit, Service Pack 1.
CPU: Intel Core i5-2300 @ 2.8GHz
Ram: 6 GB
BIOS: American Megatrends P01-A3, Build Date: 2/18/2011
Previous Video Card: 64MB Intel HD Graphics 2000 integrated graphics chip
check to see if your mb bios is up to date..may be a bios bug. with new install of windows on a pc you have to install the mb chipset drivers for windows to make the pci devices work right. in the bios make sure pci or pgeg set for the first video device and make sure if there a setting to turn on the onboard video with a gpu turn that on too. make sure on the mb the 4/8 pin atx power plug connected and if there two 6/8 pin power plugs on the video card both of them are conencted. with one the fan will turn on but the video card wont turn on.
also post up the spec of your power supply it may be under powered.