Comment 1 for bug 509632

Does AltGr+SysReq+R work and let you switch to tty2
Do you have another machine from which you would be able to ssh in after the crash (if it's not a kernel panic, e.g flashing numlock)? If you setup sshd and ssh in next time it crashes you may be able to get better linfo, maybe even find the cause using top,dmesg | tail
Have you looked through /var/log/syslog (ksystemlog makes this easier) any hints? (attaching syslog may help others find that hint)

dpkg -l kdebase-bin xserver-xorg xserver-xorg-core xserver-xorg-video-i128 && uname -mr
will pop out some useful version info