That's a bit strange that verbose mode won't work when the progress bar has progressed 3/4. If you've also tried single-user mode (command-S), and you don't have either a firmware password or filevault (unlikely, but this is Apple says to look for if verbose mode and single-user mode don't work), then the next option would be to try resetting NVRAM/SMC and/or booting from either the install DVD or a bootable HDD. Also, if you're not using a directly-connected, wired keyboard, you might want to try that.
I did a search and guess you can auto-update a beta OSX. But since you have no firm indication that was actually what happened, I would guess it's some hardware issue.