Get the diskette or CD that came with your current videocard. Then reinstall the drivers.
If that doesn't help, boot into Safe Mode, go into Device Manager, delete the video card, and reboot. Windows will see the new hardware and ask you for the drivers. Which you conveniently have at hand.
This most likely is a driver problem, and this procedure will solve it.
Kees
Our monitor looks fine while booting up but once
Windows 98 is running the coloring and size of everything is awful. When in display properties/settings there are only 2 and 16 colour to choose from. The others are no longer there.
Is this our video card??? If it is it will be the
3rd video card replaced in 3 years.......??
HELLLLPPPPP!!!!

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic