Q: Yosemite Upgrade - iMac mid-2011 - Stuck on white progress bar screen at about 50%

I used the methods in this thread and they helped. When I restarted rhe computer however same thing happend. White screen with a grey apple logo and a black progress bar. Every time I reboot it comes back. Any solution?

THank you. This worked for me too as well as what SATopwater advised.

Thanks. This worked but I did it with what Pikachu advised

none of these processes worked for me, but i was able to revert back into mavericks, and from there i did the yosemite upgrade once again and now it works perfectly fine.

Tried the safe mode thing, didn't work. Maybe because its a company managed machine and although I have admin rights, there is another admin account that controls startup items I cant access. Was going to try the Pikachu approach but went into recovery mode first and just selected Reinstall. took about 45 minutes with one reboot but now everything works fine....

thanks soooo much ... really saved me a lot of time...

SATopWater's solution worked for me, thanks!

Here's my problem, which I just submitted to Apple feedback (I will try the methods used in this thread though).

I have a late 2011 MacBook Pro, and upon installing Yosemite, my computer would not start up. When the progress bar got to slightly less than half way, the screen would go black, though I could still see the mouse and occasionally a spinning wheel on that black screen. I called support, and reinstalled Yosemite. I still got the black screen and the freeze, but I let it sit overnight and when I woke up it had gotten past the freeze and I could log in. However, the computer ran incredibly slowly, even just trying to open Finder windows. I disabled the transparent graphics, as users have suggested, but it still lagged in every task, and I saw it was using 3.9 GB of 4 GB of RAM with no programs open. Now, again, it won't start up. Countless users are experiencing the same thing.

If you have another boot disk on another hard drive start up from there and do another install.

If not, try starting up in Safe mode on your MBP.

http://support.apple.com/en-us/HT201262

First, be  sure your MBP is shut down.

If your MBP will not shut down, press and hold the power button for 5 seconds to force a shutdown.

Starting up in Safe Mode

Follow these steps to start up into Safe Mode.

Press the power button.

Immediately after you hear the startup sound, press and hold the Shift key.

The Shift key should be pressed as soon as possible after startup, but not before the startup sound.

Release the Shift key when you see the Apple logo appear on the screen.

After the Apple logo appears, it may take longer than usual to reach the login screen.

This is because your computer is performing a directory check as part of Safe Mode.

In other words, your Mac will be running slow and not everything is functional

Once in Safe Mode, go to

=====> System Pref

=====> Users & Groups

=====>Login Items

Check for any login apps you might have and remove these login apps.  Don't hide them, remove them.

Then do a normal restart.

How did you revert back to Mavericks?

So many users, like myself, got the same issue. I wonder why the Apple folks don't provide release notes and proper instructions for such a major upgrade.

Worst of all: Apple lets all their users struggle i.s.o. stepping on the plate providing professional advice how to resolve the issue.

For those who had luck with SATopWater's suggestion, two questions:

1. Does it matter whether wifi was enabled by default before you started to upgrade?  I use an Ethernet connection and normally have wifi disabled.

2. My hard drive is still churning after about 12 hours at the 50% progress bar point.  It sounds like SATopWater didn't do the fix until the hard drive was quiet. Have others attempted it while drive is still active?  I am willing to wait longer, but how much longer???

Thanks in advance -

zp

I didn't use the WiFi adapter (Airport) to perform the upgrade either.  I used the Ethernet and turned off WiFi, yet the upgrade still insisted on activating the device, thus bringing the upgrade to a halt at 50%.  Yet, I had to interrupt the upgrade process and deactivate again, the WiFi adapter before the upgrade progressed. 

Apple later on issued a fix for the problem, yet failed to admit the problem at hand.  I know this because after the fix (update) was applied, my MB Pro booted up and displayed what appeared to be the final portion of the Yosemite upgrade . . . weeks later.

Your hard drive may have a process just running around in circles.  I'd interrupt the process and disable WiFi (again) and let the upgrade proceed.

I hope that helps.

Many thanks. I just downloaded it yesterday, so if the fix was issued some time ago it's odd that it's still messed up.  Not that every Apple fix works....

Just an update - SATopWater's fix did work for me, AND I shut the thing down while I still heard noises from the hard drive (just to answer my own earlier question in case helpful to others).  SATopWater, thanks!

Installation finished in a couple minutes.