Let me start off by explaining that I am booting OS X off an external Thunderbolt SSD (I still have ML installed on internal iMac HDD). I downloaded Mavericks and proceeded to install it on the external drive but upon reboot my login password didn't work. When I put my password in which I know is correct the screen flashes white then returns to login password entry bar. After getting frustrated because I know password was correct I alt+started my computer and used Terminal to reset password to different passwords but ultimately they all resulted in the same result except for when I used a blank password. With login password set as nothing/blank I was able to double click on my username and gain access to desktop. I went through and changed password back (several times with same result) in settings. At this point I couldn't figure out why I was having this issue so I called AppleCare. Well after running through gamete of their requests I am still left with this issue. I can login and use iMac just fine with no password set but that isn't secure nor what I want. Any suggestions?