Gray screen iMac 2008

Hi
I have a iMac 24" 2008, with the famous geForce 8800 512mb
Can anyone tell my what´s wrong? I think that it´s the video card that is broken.
The computer just load like in the picture, and after a couple of minutes it restarts. Not able to get into the Mac os.

I don't have the possibility to connect it to a external monitor



Thanks
determig

I have just read that the GeForce 8800 is really crappy...
But if its the HD, do you think it can make all the noise on the screen?