How do you get the resolution to change in Xp?

I recently formatted and reinstalled windows xp on this dell computer, the thing is when I did it I had it hooked up to a flat screen monitor, now its back to its original and the task bar and icons are on 8 bit color and 1072 x 820 resolution and when i go to settings to change it the sliding bar won't move and there is only 8 bit color scheme in the drop down window, could it possibly be the monitor or soemthing else? please help.How do you get the resolution to change in Xp?
its probally the drivers for the graphics card they need updating or installing properly