Monitor help

I am having trouble getting a good picture on my 25in wells Gardener
monitor. I am running advancemame thru DOS. The screen looks really
good except for about three inches at the top of the screen. Depending
on which horizontal or Vertical way I adjust the screen the top 3
inches stretch to one corner or the other. Everything looks good on the

monitor except for the top 3 inches. When I hook up the Jamma harness
back to the NBA Hangtime the picture is perfect. So it probably has to
do with the MAME configuration. It there a prompt that I can go into to

stretch the screen or something else I can try. Has anyone else run
into this problem.

Thanks