Tried to update to El Capitan, now I can't boot at all After trying to install El Capitan and getting several notices that it can't be installed, now when I boot the computer it seems to be stuck in a login loop or something. 

Every time I restart the computer now I see the grey progress bar start as though it's doing something (with Apple logo), it goes for a bit and then shuts the machine off. 

I have tried holding Shift while powering on into safe mode, but it has no effect. I cant even boot now, just a loop. 

I have also tried using Cmd+R to reinstall OSX 10.8.5 but it says the disk is locked. I chose reboot from 10.8.5 disk, but it simply goes back to the loading progress bar loop. 

Was upgrading from 10.8.5. OSX on Intel MacBook Pro
You'll want to use the erase and install steps from:


https://support.apple.com/en-us/HT204904


Hopefully it's not a hardware error and you can just fix this with a clean erase.