You don't have the right device driver for your video card, it seems. You need to find the driver for your card, which means you need to figure out what your card is and download the driver from the manufacturer (or find your original install CD's, if you have them).

go to device manager and check the drivers for the monitor and make sure the are install correctly, no yellow? etc may be a corrupt driver and need to be reinstalled
if this is not the problem go back to display icon>setting tab>advanced button>check the DPI setting
you can try changing this, should say normal size
also use the troubleshooting tab if needed also
(Note on display properties make sure the monitor size matchs your monitor your using, drag icon to match)

hope this helps

You'll need to go to the video hardware manufacturer's website and see if they provide drivers for Windows XP.