No chime, no display(black), fan spinning, DVD drive try to run.

On my iMac 20" A1224 Early 2008 2.66GHz, I have black screen and no chime, the fan spinning, the dvd drive sound like want to run or spinning, I checked the led diagnosis lights, the two first is on, but the third blinking, the fourth nothing.

Now, this is the weird part, I have total 4GB RAM(2x2), does not matter in which slot I place the memory(one module at the time) or swapping memory, the computer chime, the dvd drive make a normal noise when computer is starting up, but still black my screen, and the led lights only the two first remain on, but the third is not on or blink, and the fourth nothing.

I purchase an adapter cable(mini dvi to DVI) to try with an external monitor, with not successful, none, this computer has AMD video card, I was suspecting that is the problem, but when I try run the computer with only one memory module, the computer sound like is working, but not display, at the other hand, with two memory modules computer no chime, no display and dvd drive noisy.

I am very frustrated, I can't find any solutions, I am asking for help.

Thanks

Marco M.