new Video Card loses sync on ME

I have a compaq presario with a 2x AGP nVidia Vanta based
card that I am trying to upgrade. I bought a nVida GeForce
FX 5200 PCI card and plugged it in (to one of my scarce
PCI slots, unplugging the AGP).
The computer detects the card and then the monitor, I load
the drivers and all is well at 640x480x16 colors, but soon
as Windows loads at anything else it goes through the
Windows Logo screen, flashes the Background text window
then the Monitor drops back to Stand-by and I have to
reboot blind.
I have tried my darndest to delete the existing drivers,
do I have to do this file-by file or is there an easier
way?
Would manually deleteing incompatable lines in the Card's
registry settings stop windows from using these?
Should I just take the card back and part-swap it on a new
motherboard?
Any help appreciated.