When I hear this i think of the video cable not being perfectly in place. Usually its the VGA cable, they cant take being twisted at the connector side very much. If you push on or move the cable around (carefully) and the screen bounces between good and blue-ish then thats the problem. Its a good idea to turn the monitor OFF anytime you disconnect or especially reconnect it to the PC; then take the connector fully OFF at each end one at a time, then push it back on as much as it will go, then use the screws to lock it down, then power back on and try again.
sometimes trying a different monitor will work because of the VGA cable being intermittent and you think OH its the monitor but it wasnt.