Do Start / Run / MSConfig and make sure Normal Startup is selected. Choose
Advanced and make sure VGA 640x480x16 is NOT selected. Do Start / Settings /
Control Panel / Display / Settings / Advanced / Adapter and note the adapter
description.  If this is some type of generic VGA driver, or if it doesn't
exactly match the adapter installed in your machine, then you need to find
and install the video adapter drivers specific to your particular hardware.
These should be available at the video adapter card manufacturer's www site,
or if the video adapter is integrated into the motherboard then it should be
available at the motherboard manufacturer's www site.  You may have been
provided with a CD as part of your system deal - in that case the drivers
should be on that CD. If you have upgraded your video adapter since you
bought the machine then the upgrade should have included a CD that would
have the drivers on it.