Q: OSX El Capitan Wont Boot
Hi. I have El Capitan and Windows 10 installed on my macbok pro via bootcamp. This morning I tried starting my computer to OS X and it loaded the status bar under the apple logo and shut off. That's all it does every time I try to start it. Windows 10 boots fine. That's what I'm on now. When I booted to verbose mode it says "disk0s2 I/O error. The volume OSX Yosemite could not be verified completely." And then some other stuff. Does anyone know what's going on here? Im going to try running disk utility next. 
MacBook Pro, Mac OS X (10.7.3)
Posted on Aug 2, 2016 12:02 PM
That error means either:
- The disk got corrupted and can't be repaired because of a software problem
or
- The disk has physically failed.
- Boot to Recovery and repair the startup disk
OS X: About OS X Recovery - Apple Support
https://support.apple.com/en-us/HT201314
- If it is repairable reinstall the OSX.
How to reinstall OS X on your Mac - Apple Support
https://support.apple.com/en-us/HT204904
- If you do not have a backup use disk utility to restore the internal disk to an external disk so you can try to recover data.
Then format the startup disk and do a fresh install of OSX
Posted on Aug 2, 2016 12:06 PM