Q: start upafter update issues

- If you do not have have a backup best is to attach a USB HD that can be erased

- Boot to Recovery

About OS X Recovery - Apple Support

- and then install OSX on the external disk. Then boot from the external disk and try to recovery data for the internal disk.

- If necessary Try a disk recovery app:

Top Ten Mac File Recovery Review 2015

http://www.cisdem.com/resource/mac-file-recovery-review-2015.html

you may be able to download a demo of Data Rescue 4, and the demo will give you an idea of what it can recover. If it looks promising, you then can buy the software.

http://www.prosofteng.com/products/data_rescue.php

- Then try repairing the problem disk via DIsk Utility. If repairable see if it work. If not the try erasing the disk and install ing OSX. If necessary replace the disk