Re: Switching video cards...
Hmmm, shut it down? If it was me, here's what I would do:
Turn off PC. Take out the monitor cable from the back of the motherboard. Open case panel. Insert new video card, screw it in, connect power if necessary. Close panel. Plug monitor cable to back of new video card. Power on. Wait to boot into Windows. Install video drivers. Change video settings as needed to personal taste.
*Fact: Microsoft Window's Blue Screen of Death vs Computerforums.org's White Screen of Death. Which is worse?