I would have thought that your on-board graphics would have been adequate for what you are trying to do - but that's a different matter. Either you have a faulty card or a faulty AGP slot on your MB. Try to eliminate the card problem first. Have you contacted the vendor technical services (as its OEM I doubt the manufacturer woould be interested)? Do you have a friend with a AGPx8 mb where you could test the card?
Alternatively, if you can get hold of another AGPx8 graphics card that you know is working, see if that works in your PC.