Created on: March 20, 2015
Last updated: April 16, 2015
If your Mac is randomly getting stuck during the boot process in Yosemite, it may be from unsigned extensions. This is most common with the Mac mini models.
First you will need to get it to boot before we can proceed.
Getting the Mac to boot:
1) Start the machine while holding down the Option-Apple-P-R keys
2) Wait until you hear the 3rd startup chime, then release the keys.
3) If that doesn't work try an SMC reset here: https://support.apple.com/en-us/HT201295
Now for the fix after you get the machine to boot:
1) Open Terminal in /Applications/Utilities
2) Enter "system_profiler SPExtensionsDataType > ~/Desktop/kextList.txt" without the quotes and hit return(this will take a while to run).
3) There should now be a kextList.txt file on your desktop, open it and press both the "Apple(Command)" and "F" keys to bring up the find.
4) In the find field insert "Obtained from: Not Signed" Copy the destination to the .kext file to a list for use later. (Click next to cycle through all of them.) Example: /System/Library/Extensions/JMicronATA.kext
5) Browse your drive to /System/Library/Extensions and remove any of the unsigned kext files.
6) Reboot and you should be all set.