Boot to Grey Screen, but blank

I've been trying to read for a good hour or so, both here and on the apple forums. My case seems different, in that when it boots, it boots to a blank grey screen, I never get any logos or pinwheels.

I have tried all of the tricks, etc, but the computer will not register any inputs. The ONLY thing it will do is very quickly power off if I press the power button.

I do not know exactly what happened, as there is family in town and lots of different people on the computer.

I do recall yesterday that some updates were going to install, but someone had configured OSX to restart under windows xp with boot camp. So it tried to install updates when shutting down but booted to windows.

Since then, the computer would start back up but if I held down the option key it would just give me a blank grey screen with a mouse pointer, but not let me choose OS to start.

So I let it boot into XP without hitting option key. XP loaded ok, I tried opening the bootcamp options menu in XP and selected restart in OSX. Now it is to the point where it's stuck.

Thanks in advance for any help you can give.

Quick update.

Just for the heck of it I just tried to start it up and let it run. It ran for about 10 minutes and booted into XP. I had tried through my trouble shooting to boot with the OSX cd and that didn't work.

Guess I'll try using boot camp control menu within XP to boot to the OSX CD.