I have a 2010 Macbook Pro running the latest version of El Capitan.
I recently did an update and ever since then when I boot up I get a prohibitory symbol. I tried reinstalling El Capitan using a USB drive, but once it reboots it tries to go through the installation process again. When I take the USB stick out it gives me the prohibitory symbol.
I tried to restore to a time machine backup from a time capsule using two different dates.
The first restore attempt was to a date when I first installed El Capitan. That resulted in it saying there was already a corrupted version of the OS and it couldn't restore. So I formatted the hard drive and tried again, it resulted in a prohibitory symbol.
The second restore attempt was to a date right before I installed El Capitan and was on I think Mountain Lion. That resulted in a file showing a question mark in the middle.
What should I try next?
Edit: I installed an SSD in this two months ago and the S.M.A.R.T. settings are fine.
Best Answer
It was a bad sata cable according to the genius bar. They switched it out and it now works!