Broke my Radeon 8500?!?!

I think I may have damaged my vid. card by overclocking it too much. The thing is I had exchanged my MOBO for a new one because there was something wrong with it. When I got a new one from the RMA dept. in California, I assembeled it and tested it out. Now whenever I try to boot up my computer, my system locks up and goes nowhere. When I disable the device in the Device Settings, it boots up normally into windows xp. Is it my card, or is it my motherboard? I tried looking at the IRQ settings and there are no conflicts with any type of Address assigned on the motherboard. I have no other AGP device to test out the slot so is there any other way to test it?

Thanks.