Make sure that any other vid card drivers are removed. You may need to get a "driver cleaner" to remove all of the old drivers. Some one from [H] turned me on to one from www.drivercleaner.net with out it there may still be some crap left behind that a normal unistall will leave.
Also I'd look in the bios to make sure that it is looking for a pcie card. Mine (also an Asus) has options for onboard, pci, and pcie. I have mine set to first use the pcie, but if no card is installed it will then use the onboard.