G550 fails again

I put a USB2 board in my daughter's PCI bus and it crashed the video.
I took the new USB card out and the video still didn't work, but after
I turned the computer off and on a few times it started working again.

Then I put the USB2 board into my own computer, to see if it would
crash the video. It didn't. My computer just booted right up and
said it detected new hardware, and the new hardware was now ready to
use. (Jeez, I love XP.)

My daughter's computer and mine are identical. I built them both
myself. Same parts list. Same OS (XP SP2). We both have a Matrox
Millennium G550, and I've never had any problem, but hers crapped out
after only 2 years of service. Figuring it was just a fluke, I
replaced it with another of the same (about $130). That was only a
few months ago, and it's been working fine. Now I put in a PCI card
and the video crashes again.

This time it recovers, but why did it crash? Mine didn't crash. Do
you suppose Matrox is having a QC problem? Do you suppose my
dauther's motherboard (Intel D845) has a flaw? Am I missing
something?

Why would a PCI card crash an AGP video? Help?

Problem solved.

I hang my head in shame.

Videocard not fully seated in socket.

Sorry, folks.

Carry on.