My Mac (MBP) won't get past 30% on the progress bar at startup. Then after a while it reboots itsef and the same thing happens. I tried to boot in recovery mode, safe mode, reset nvram, and still the same thing happens. I have a Yosemite Install USB and I tried to start from that (held down Option Key and chose the disk), however, the same thing happens, the progress bar gets to 30% and hangs.
I can start in single user mode, and I have tried fsck and nvram reset there, among other things.
So now I'm wondering if its possible to reinstall the OS while in single user mode. I have mounted the Yosemite Install disk in /Volumes/usb. Any help, or other suggestions appreciated.