Need Help! fadal vmc 40

hello there I have a fadal cnc 88hs/88 we purchase this machine three years ago we replace the monitor because the old one was broken once we change the monitor we start up the machine the monitor work for a little while and then the monitor went blank we also check the graphics board and we replace it with a new one but still I did not get any graphics
or video coming from the monitor we also check the rest of the boards in the control box all of them seems to be working alright as far as the voltages are concern now is it possible we overlook something please advise