Maybe you can try to uninstall the current drivers of your video card and try to install the latest drivers from Evertop and if the issue persists you can try downloading the latest driver from Nvidia for the 9400GT GPU.
About the onboard video not working, this is because Intel chipsets with onboard graphics will automatically disable the onboard video when the PCI Express bus is populated by a video card. This means that everytime that you install a PCI Express video (x1, x4, x8 or x16) the onboard video will be disabled.
If you have the option, try to test another video card, in that way you can determine if it is something related with the video card, the motherboard or could be just that they are not compatible eith each other.
Holy cow I'm having same problem. Thing is I had this card working just fine on windows xp. Now that Ive updated to windows 7 my computer isn't reading the card right. I can still use the card for display but in device manager it doesn't show up. Also the drivers will not install either because my computer isn't recognizing the card. Ive tried everything I can possible think of. changed settings in bios to pretty much every combination I can think of. Its weird because the card is displaying my video but at the same time the computer isn't recognizing it.
I got an hd5570 vid card
to the point where i think either the pci-e slot is jacked up or vid card is messed up because nothing adds up here.
well from what i'm reading my mobo might not be compatible with windows 7 which is what could be causing this error?