Wait: You have been trying to BOOT this thing, right? Not simply wake it from sleep?
If the screen is gray and nothing happens, you need to turn off the machine by pressing and holding the power button. Then press it again to start up the machine.
If that is in fact what you've been doing, I doubt this will work, but:
Stick in the original Install Disk that came with your Mac, restart the machine, and hold the "D" key. This should boot the Hardware Test.
Run that if you can.
Frankly, it sounds like there is nothing we, or you for that matter, can do to help the situation.
Take it in for servicing.