Which part is failed on my iMac with white screen?
Upon boot, white screen comes on, boot sound plays, not much else. Tried resetting PRAM, and unplugging from power and starting with nothing plugged in, with only keyboard, only mouse + keyboard, booting off of install DVD (which seems to work because I hear the disc spinning and being accessed and the screen dims after several minutes of activity, then comes back to bright when I move the mouse, but screen stays white).
Pulled hard drive and verified that it hadn't failed. Reformatted in another mac and attempted to re-install OS X, but can't because of white screen.
I think it is either the logic board, or GPU, but I don't have a lot of experience with Mac hardware, so I wanted to make sure I'm not overlooking a common iMac problem.
A1224 (EMC 2133)
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Control-Option-Command-8 failing that, try booting in other user accountstry plugging the monitor in after its booted uptry booting it in safe mode does it still occur? failing all of that try resetting the PRAM/NVRAMhttp://support.apple.com/kb/ht1379
You may need to reset the PRAM. Start your computer and hold down the option, command (apple), P and R keys simultaneously until you hear the second chime. Then release.
This will reset the perimeter RAM (PRAM) and may allow your system to start, which it will do immediately if it capable. If this is not the case and you have already tried removing the RAM and the HD, you may need to have the motherboard tested.
A question mark on the boot screen is an indication that the machine can't find your boot drive. Usually this is trivially fixed by resetting the PRAM (holding down command-option-P-R after turning on the machine with the power button, until you hear the chime three times).
However, taken in conjunction with your other symptom, I would suspect a failing drive or a failing SATA channel (less probable). Does it boot from the original DVD without these symptoms? After booting from the DVD, are there any indications from the tools that the hard drive may not be showing as present, or may show intermittently?
If you have a good backup (Time Machine or otherwise), I would erase and reformat the disk with "write zeroes to all records one time," then reload the backup, and see if that fixes the problem. If not, you will need to replace the drive, and reload the backup (hope you have one) onto the new drive.
try resetting the SMC and the NVRAM. This occasionally stores the startup state and any keystrokes used during boot. Common issue with all intel macs.
Resetting PRAM and NVRAM
1. Shut down the computer.
2. Locate the following keys on the keyboard: Command, Option, P, and R. You will need to hold these keys down simultaneously in step 4.
3. Turn on the computer.
4. Press and hold the Command-Option-P-R keys. You must press this key combination before the gray screen appears.
5. Hold the keys down until the computer restarts and you hear the startup sound for the second time.
6. Release the keys.
Your computer's PRAM and the NVRAM are reset to the default values. The clock settings may be reset to a default date on some models.
To reset the SMC on an iMac
1. From the Apple menu, choose Shut Down (or if the computer is not responding, hold the power button for approximately ten seconds until it powers off).
2. Unplug all cables from the computer, including the power cord.
3. Wait at least 15 seconds. The SMC reset occurs automatically once the iMac has been unplugged from the AC power source for several seconds.
4. Plug the power cord back in, making sure the power button is not being pressed at the time.
5. Reconnect your keyboard and mouse to the computer.
6. Press the power button on the back to start up your computer.
Note: The iMac does not have a button on the main logic board for resetting the SMC, which eliminates the need to remove the computer?s cover to reset it (as required for some other models).