I've installed El Capitan Developer Preview . Installation crashed at about 75% and then i could only boot in safe mode.
I wiped all the hard drive to reinstall Yosemite but it only displays 10.11 as an installation option. However, installing it won't work either. It says this disk is locked (the one I just wiped).
Now I can not even unmount it again.
I tried in the Terminal to erase it, won't work either.
Anyone else having these issues, or has any clue how I can solve the problem (install Yosemite)?