Power problem

Hi

First time posting here. I'm a Mac guy but I'm trying to fix a problem
with the wife's PC.

When starting her computer today, there was an error message about the
Radeon 9800Pro video card not connected to the power supply.

I knew the card had been connected ever since we had that PC built, 46
months ago but I nevertheless opened the case and checked carefully and
indeed the connector leading to the power supply, was tightly inserted
into the proper slot.

I replaced the video card with an old Radeon 8500 and voila, my wife
can use her PC again.

Now, my question ! Since the whole PC has power, I know it's not the
power supply. How do I determine if the problem lies with the connector
that goes into the card or if the video card is toasted ?

thanks