Monitor goes blank , power light goes off.

Question

I have a Polyview V17E LCD monitor and the screen goes blank at different times . The power light goes off also. The first time I unplugged the power supply and it restarted , but now I can unplug data cable and power cable and it will not restart . The only way to restart monitor is to turn off computer and restart computer . Do you think it is a monitor problem or a computer problem