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1. Shut down the computer. 2. Plug in the power adapter to a power source, connecting it to the Mac if its not already connected. 3. On the built-in keyboard, press the (left side) Shift-Control-Option keys and the power button at the same time. 4. Release all the keys and the power button at the same time. 5. Press the power button to turn on the computer. 6. Press and hold the Command-Option-P-R keys before the gray screen appears. 7. Hold the keys down until the computer restarts. 8. Release the keys.
If your not getting the Startup noise ( the bong) then something your hardware has failed as that noise indicates hardwise everything is ok.
I would start with new ram and see if it gives you the same error.