So when I boot my mac up (dual 1.8 ghz 2GB ram) the light above the power button comes on, then turns off. There is no boot tone, but the HD spins up and the fans run, but there's no video output. I have reset the SMU, checked the ram and video card and cleaned the system. Still nothing. I've tried it with different monitors and disconnected all peripherals. Last time it was working the fans spun up to full speed and the system froze up it hasn't turned on since. Forums say its likely to be a failed logic board, can anyone help?