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
download 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.