There is a comboTV box & a Dell monitor. When they plugged & powered, the monitor says "monitor is in powersave mode, activate using pc" in black background.
But the comboTv box works fine with another LG monitor. Also the Dell monitor works fine with the PC.
If you have a menu on the monitor, find reset menu and do it. It might fix your problem. If you don't have such an option, then you would probably have to go for a different monitor.