iMac white screen

For 10.4 thru 10.6, see > Mac OS X: Gray screen appears during startup

For 10.7 and later, try > OS X Mountain Lion: If you see a gray screen at startup

This is my tale of “Nightmare in White” in the hopes it may save others time and money. The machine is an iMac, late 2009, OS Yosemite 10.10.5

I keep my iMac on all day. One afternoon I checked the screen and it was totally an off-shade white with nothing showing but the cursor. I shut down and restarted. Same result. After trying this a few times I knew there was trouble. I called an Apple Store, but could not even get to a human without a $29.99 payment. Geek Squad was higher, with diagnostics running as high as $79. So I started out on my own.

I spent about 10 days on and off doing research and experimenting. Most of the information I found was not correct or esoteric (at least for my machine). Had I known what I do now the process would not have taken more than an hour.

First thing is to run the AHT (Apple Hardware Test). This is run from the applications disk that came with the computer. You cannot start it from the hard drive in this situation. The test found no hardware problems! I had always expected the hard drive. To diagnose this I needed the disk utilities from the installation disk that came with the machine. So how do I get the apps disk out since nothing is working? Many various methods on the Internet, but the simplest one worked: Shut down and hold the mouse key down and restart.

The instructions were to hold down Ctrl c to access the installation disk. This did not work. Just holding down the c key did! Disk utilities found the hard drive, but “couldn’t mount.” Hhmmm, must be hard drive. Next step start in safe mode. To do this I had to hold down the shift key at startup for what seemed like two minutes.

In safe mode everything worked that you would expect in safe mode. I then made a disk image to the desktop. I did a restart and fully expected that I would get the white screen again, but lo and behold everything was back to normal and all working! I have no explanation for what happened, though I still suspect the hard drive is the problem. I have had the machine on and off a several times since and all is still working.

I will replace the hard drive myself if I run into further problems. This is a fairly easy procedure and U-tube videos are available. Of course if you have no experience with exposing the guts of a computer you are likely to be intimidated.

If anyone can comment on what happened I a sure all would appreciate it.

Good luck!