Chosen Solution
Since I installed the last Yosemite update (Version 10.10.5), my iMac will not fully boot up! When it starts, the boot screen (Apple logo) and a progress bar appears. The progress bar fills up until its about 2/3 full then nothing happens. I have let it sit for days to see if it will finish booting and nothing happens. I have also tried the boot-up shortcut keys and nothing happens. Can anyone tell me why this is happening? Will I need to upgrade my CPU?
Do you have access to a second Mac? Are you able to get your system into Target Mode and then connect it to the other system via a FireWire cable. If you can see if you can run Disk Utilities - Disk First Aid does it pass? You also might have a North Bridge chip failure if you can’t get the system in Target Mode. At that point you’ll need to think things through do you want to replace the logic board or put the money into a new system. If you have stuff on your drive you can take it out and use the IFIXIT Universal Drive Adapter to connect the old drive to your new or alternate Mac system.
There is a way to get into separate screen on the boot up, there you will find drive settings and such, this happened to our Mac. And I watched a video on how to do it. If you just research it some more on how to get the the boot setup screen that should fix it. Keep us posted.
