I had the same problem though with a HD2600 AGP version. I ended up swapping
my power supply with my brothers computer so that I could connect the 6 pin
power connector that my old power supply does not have. After using the
supplied 24 pin to 20 pin converter it all worked.
Unfortunately my brothers computer no longer worked as the power supply I
swapped did not have a PCI express 24 pin connector required to power his
mother board. He does not require any external power on his video card.
No problem though, the next day I bought a 700 watt power supply, the same
one that he had in the first place.