No Signal Problem

Hello,

So I've had my PC for about two and a half years, and I came back from this month long trip to find that my comp turned on, but my monitor wouldn't respond. When I press the power button on the Acer monitor, it turns on, displays a "No Signal" message, and then turns off. I swapped out the graphics card, the monitor, and the cable, but nothing changed. I took the RAM out and put it back in, still nothing. I tried the method of unplugging the comp and holding down on the power button, no dice. Any ideas?