HT1379 My iMac won't start up. I turn on the power button the start up screen appears. The apple symbol shows up, the loading shows up, the loading circle starts. Then the loading bar disappears, and The loading circle and apple logo disappear and power i

Question

The power comes on. Screen turns white. The start up sound plays, the apple symbol come up the loading bar show up but do not show any sign of loading. The loading circle appears and spins. Then the loading bar disappears and the. The screen goes black and power goes off. I've tried unplugging, command alt escape, and command alt p r,  no effect.  Any other suggestions???

Answer 1

OS X v10.6- Gray progress bar appears under Apple logo during startup
Install or Reinstall Lion/Mountain Lion from Scratch
Be sure you backup your files to an external drive or second internal drive because the following procedure will remove everything from the hard drive.
Boot to the Recovery HD:
Restart the computer and after the chime press and hold down the COMMAND and R keys until the menu screen appears. Alternatively, restart the computer and after the chime press and hold down the OPTION key until the boot manager screen appears. Select the Recovery HD and click on the downward pointing arrow button.
Erase the hard drive:
  1. Select Disk Utility from the main menu and click on the Continue button.
  2. After DU loads select your startup volume (usually Macintosh HD) from the
      left side list. Click on the Erase tab in the DU main window.
  3. Set the format type to Mac OS Extended (Journaled.) Optionally, click on
        the Security button and set the Zero Data option to one-pass. Click on
      the Erase button and wait until the process has completed.
  4. Quit DU and return to the main menu.
Reinstall Lion/Mountain Lion: Select Reinstall Lion/Mountain Lion and click on the Install button.
Note: You will need an active Internet connection. I suggest using Ethernet if possible
            because it is three times faster than wireless.