wrote:
I have a 19 inch monitor.

Until this AM all four sides of windows filled the monitor screen
nicely. Now suddenly I have a 1/4" black area on left and right. My
monitor's manual controls seem inoperative, so I cannot expand the
raster that way.

Is there a way, using W98SE function(s)?

Thanks

This has nothing whatsoever to do with the OS. Suggest you RTFM and learn to
use the OSD controls.