I went through a routine weekly update and system displayed Apple progress bar page. Then message said system would reboot after a few minutes. The screen went white and nothing happened for over an hour. Tried rebooting and got Apple progress bar page, which proceeds for about a fourth of the progress bar then screen turns white and nothing happens for hours. Have tried this 3 times and same thing happens. I recently got a new mother board, maybe 2 months ago. Anyone know what might be happening and how to fix?