QUESTION: Is it the monitor or video card or software problem?

My monitor display fades to black occasionally, taking 2 to 3 seconds to
fade out.

Computer still functions, but can't see anything on the display.

The monitor "on" light remains on, so it always has power, and turning
monitor on/off doesn't regain any display.

Warm reboot won't bring back the display.

Cold reboot after waiting a few hours brings it back, until today: cold
started the computer and display is dark.

Do I need new monitor or video card or is it software related?