my crt monitor display did not fit the usual screen setting.it became very thin at the centre of the monitor.i tried resetting the visual using monitor button..but no change..I knocked hard on the upper side of the monitor,,then the screen got back to normal view.if i wnat to use the monitor,i must knocked its head,so i can see what were displayed.if not,,the displayed will be very thin and small..whats the cause of my pblem?help meee..