Flickering And Multiple Images On Monitor

please, i have a monitor that flickers each time i turn, it on. but if i hit it not so hard on the head it stays normal, i know this hard way can never solve the flickering and multiple images been displayed. i want a more experienced engineer to help out here. thanx

NB: the monitor is a tv/monitor screen, i use it for both functions. even with tv external arial, it still fumbles.