Folder with question mark displayed during upgrade to 10.10.3 reboot
During the reboot portion of the upgrade to 10.10.3 a folder with a question mark appeared blinking on the screen. I looked around the internet and saw a couple of solutions. All didn't work with the most radical being a fresh install. I was able to boot up by powering down, then holding the Option key while powering up and selecting the computer to boot from where it took me to the login screen. This worked but I would prefer a solid solution.
MacBook Pro, OS X Yosemite (10.10.3)