loss of display settings during boot

several times in the past week when I boot up, my display
settings are lost and set at "four color". sometimes
rebooting fixes it and most of the time I have to
reinstall my video drivers to achieve the highest settings.
This usually happens after the computer has been off over
night. I don't understand why this happens or how to
remedy the problem. This has only happened recently and
the computer is two years old. I have an Athlon XP 1600+
processor, 512 pc2100 ram, Geforce2 MX/MX400 video card.