Agree with max reverse, probably resolution change (800x600 to 640x480) or such. Assuming you have win95/98, right click on the desktop and select properties/settings/screen area(Win98). Drag slider to next higher res. Gen 800x600 for 15inch monitors, 1024x768 for 17inch monitors, etc. Don't forget to "apply" the change.
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When all else fails, read the manual!