Chosen Solution

My first gen 1.1 mac pro wont boot up. When I push the power button, the light flashes on and off, the fan comes on high and just continues to run but wont boot up. It’s done this once in a great while from time to time. In the past, I would hold the power button in until it shut off, then push the power bottom again and it would come on and boot. But now it just does the same thing. I push the power button, the fan comes on and just runs continuously, never booting up…

What are the diagnostic LEDs telling you? The two main things that I have seen fail on the 2006-2008 are

  1. the video card (which does not appear to be your issue) and
  2. the Power Supply ( which does appear to be your issue). Usually a failing power supply will begin with unexplained restarts before completely failing.