Monitor or graphics card - which is the problem

I've got a new home built computer being used with a Princeton Graphics 17" monitor. Periodically the monitor goes black (as if it had no input), yet the computer continues to run. If I reboot the computer, the monitor remains black. Yet if I unplug the monitor from A/C and plug it back in, Windows shows up again on the monitor. And sometimes it doesn't go totally black, but black with faint outlines of Windows being visible. Once again, if I remove the power cable to the monitor and plug it back in, Windows is completely visible. I tried the monitor with my laptop, but couldn't replicate the problem. I contacted a local service center and they think it's a bad mother board.

The next time the monitor acts up, instead of power cycling the AC to the monitor, I'm going to disconnect the monitor at the connector at the back of the computer and reconnect it.

If the monitor comes back to life like it does with an AC power cycling, what does this tell us?

If the monitor stays dark, then what does this tell us?