Please remove the three screws in the bottom of the frame and remove the housing. Press the reset button on the power supply located at the bottom of the frame where the power cord plugs in. You should also note two rest button about the middle of the motherboard just to the left of the diagnostic LED lights. Plug it in and press the top one with the eraser tip of a pencil. This resets the PRAM. Pressing the bottom one restarts the computer. Note the condition of the diagnostic lights and tell us which ones are on to see where to look next. Look at the 24 capacitors (the small cans) on the motherboard and see if any are corroded and/or bugling.