Just FYI, same thing happened to me, twice !?!
Virtual Box, LAMP, did all as per quick start guide. No errors reported, could log in externally via browser to webmin, phpmyadmin etc.
(2nd time, took a 'snapshot' at this point
Installed and startx'd ubuntu 14.04 lts desktop; entered username bitnami and mypassword, but the machine 'did something' (black screen & resized virtual box) though wouldn't let me in.
Solved by logging-in as guest, opened terminal, "su bitnami" and then AGAIN "sudo chown -R bitnami:bitnami /home/bitnami/.*"
BTW I'm a total newbie to linux, reliant on mindlessly following guides, so rather disconcerting.