a) - did you specify that it should be compatible with your chipset when you made the purchase?
b) - can you telephone them? Write to them?
You may find that if you want to swap the ATI card for an nvidia they may be helpful but I don't think that you have the right to get a refund unless it is within 7 days of taking delivery. If it is within the 7 days you may well be able to return it during the "cooling off period" as prescribed in the distance selling regulations.