I have been trying to get my mac to boot for days now. When I power it on the apple logo comes up with loading gear spinning. Eventually it stops spinning and doesn't go anywhere. I have try to boot to techtools with no success. Tested HD externally showing 4 bad sectors. So thought hd was reason. Put in a Samsung 500gb ssd. Tried to boot from cd to reinstall os with same result. Don't know where to go from here. Any ideas would be helpful thanks!