Q: iBooks won't open on el capitan 10.11.6

Hello mcgalla,

Thanks for that info and choosing the Apple Support Communities. I know how important getting iBooks working is to you! If I understand correctly, you are unable to get iBooks to open at all. I would recommend starting with some easy steps, before moving to more intensive steps. Here is what I suggest:

1. First, try running a quick test with the built in Disk Utility tool, as this can correct simple issues like you're experiencing.

Disk Utility (El Capitan): Repair a disk

2. Next, use Safe Mode to start up your Mac so that it performs certain checks, delete system cache files, verifies your startup disk, and attempts to repair directory issues if needed. Then test if iBooks opens in Safe Mode, and if it does, then restart normally and test iBooks again.

Try safe mode if your Mac doesn't finish starting up

Limited graphics performance in OS X recovery or safe mode

3. If you're still having an issue with iBooks at this point, you can figure out if unexpected behavior is related to user file or setting by trying to reproduce the issue from another user account. This process includes creating a new user account, logging in to it, and testing for the issue.

How to test an issue in another user account on your Mac

Cheers!