Comment 5 for bug 540632

I'm not convinced that this is the same as bug #539730, particularly since you say you can't hear the login sounds, which indicates that something has locked rather than nouveau simply mis-driving the display.

It would be ideal if you could ssh into the laptop while it's doing this and copy dmesg and Xorg.0.log. I know that's likely to be difficult, so an easier thing would be to boot the laptop without modeset=0, wait until the laptop locks, and then restart. You should then be able to attach /var/log/Xorg.0.log.old and /var/log/messages, which should contain the information from the previous boot.

/var/log/messages can sometimes contain sensitive information, so I'm marking this bug as private.