Folder with question mark displayed during upgrade to 10.10.3 reboot

I'm having this issue too, but my company has a firmware password set so I cannot even get as far as you did. Hopefully there's a more graceful solution.

Tim

boot into recovery mode CMD+R (not CMD+Option+R !)

got to Disk Utility

select and repair your Hard Drive

reboot.

You have EFI password enabled.

Just boot the mac with option key and enter firmware password when requested, you should get the startup disk chooser and be able to boot.

After boot go into Systtem preferences -> startup disk and select the startup disk.

Amedeo

I'm having the same issue as the original poster. When you say "boot the mac with the option key" do you mean when I restart my MacBook I hold down only the option key?

yes