Why are my display options so limited?

Hello,
I was recently having problems with my PC (turned out to be a full temp folder) so I used the Win 98 disk to run repairs on the Operating system. When the PC restarted I was stuck with a 640*480 resolution and 16 colours. Normally we have a much higher resolution and "true colour." I can change from 16 colours to 250 or "high colour," but when I do this and restart for the effects to take place nothing happens. Same with the resolution however I only have three resolution settings to choose from when we normally have many more.

My PC is one of those anoying packages with everything built on to the motherboard, but I installed a graphics card a while back (nvidea riva TNT2 model 64/model 64 pro). The Device Manager says it's working fine, but i tried to reinstall the drivers (from the card's cd) anyway. Apparently I've got the best driver possible.

Please help me I'm sick of these massive windows and pixelated pictures.
Jimdivine