Odd monitor problem.

I don't know why this happens and for me this seems very odd. I have my monitor placed on a wooden desk (obviously) and everytime I place something heavy on my desk, it sets my monito into semi sleep mode.

When I mean semi sleep mode, I mean this: The monitor turns a very dim gray, darker at the bottom where the dock would be and the power symbol flashes on and off. However, you can still move the mouse, access files etc. and it doesn't turn off this "sleep" mode.

What's going on?

 

Yes, all the monitors are plugged in properly.

And the monitor is a 17" Flat Screen Display. I bought it when I bought my G5 in 04.