You might need to delete all of the old video drivers.
Set your video to the basic Windows drivers.
Un-install the 3dfx tools
Right click "my computer", device manager, remove your current video card,
DON'T RESTART YET.
Open the registry
Find this key folder
If you find your old cards manufacturer(s) listed, delete them too.
Find this other key folder
Delete ALL the numbers inside this folder (Ex. 0000, 0001, 0002, etc.)
Look in the C:\Windows\Temp\ directory, I dont remember exactly where,
for the .inf file(s) for your video card(s) and monitor and delete
them. If you cant find them, dont worry, Windows will. When you start
to install the new drivers and Windows wants to use something from
C:\Windows\yadda-yadda, thats the place. Seek out and destroy.
Restart and re-install the V5 and the "drivers" for your monitor.
If you have Clean sweep, it may find some orphans you can delete now.
That should clear up any old driver issues you have.