1. I am unable to boot to recovery mode using 'command R'... nothing happens and it goes back to the apple logo and a progress bar that get to a third of the way and stops.
2. I am able to press 'option' during boot and get 3 options for loading (system, recovery, and a Yosemite install disk i made on a USB). selecting any of these options returns me to the apple logo and the progress bar that gets stuck at a one third complete.
3. I am able to select safe and verbose mode. the machine will sometimes get all the way to "system up time in milliseconds" before it reboots.
4. I am able to boot to single user mode. I have run '/sbin/fsck -fy' until it no longer displays 'modification have been made' and it displays 'volume appears to be ok" (takes 2 runs). from here i have tried both rebooting, and exiting, both result in the white screen with the apple logo and the progress bar getting to a third of the way.
5. i have tried clearing the NVRAM
6. I don't have another mac with firewire or thunderbolt to try targeted disk mode
7. i have had 1 success in getting to the log in screen using verbose mode. during the boot there was a whole screen of the same line repeated many times, it said "BUG in process suhelperdt: over-released legacy external boost assertions (1 total, 1 external, 0 legacy-external). after i logged in it reported that the system has un-expectedly shutdown, and that it would send a report to apple (is this a kernel panic?). i hit yes and then show the details. then the system hung up, and rebooted. then hung up again during boot with the same "BUG" message above.
I've got good time machine backups, and don't mind doing a complete reload if i can ever get to that option.
Thanks in advance for the help.