OS X Yosemite 10.10.4 upgrade is not completing! Apple Logo and Progress bar stop then disappear about half way through!

Processed 10.10.4 updates last night. On reboot Apple and progress bar came up and about half way through they both disappear and I just go to a white screen. Was able to reboot and hit shift and get to a safe mode but then am prompted for username and pwd that is not working no matter what I try.

Then I rebooted into recovery mode? Ran diag against hard drive and it was fine. Ran diag against the file permissions and it found a few issues. Repaired those. Rebooted - same issue.

Need suggestions on what to try next. I have Time Machine in my back pocket but would like to reserve a full system restore as my last resort.

iMac "27 (2011)