Fresh install of ubuntu 12.04 on a dell T7400 workstation: crash to login screen

I have just put on a fresh install of ubuntu 12.04 (set up as dual boot with windows 7) on a dell T7400 workstation. I am getting periodic crashes out to the login screen. I have not yet found a clear cause - i.e. the crashes do not seem to be obviously related to any single activity. A copy of the /var/log/syslog for the period covering one of the crashes ( and my logging back in) is appended below. Any advice would be much appreciated.

  Sincerely,

       Simon Morris

May 11 12:15:49 simon-Dell-T7400 goa[3571]: goa-daemon version 3.4.0 starting [main.c:112, main()]
May 11 12:16:36 simon-Dell-T7400 dbus[841]: [system] Activating service name='org.freedesktop.PackageKit' (using servicehelper)
May 11 12:16:36 simon-Dell-T7400 AptDaemon: INFO: Initializing daemon
May 11 12:16:36 simon-Dell-T7400 AptDaemon.PackageKit: INFO: Initializing PackageKit compat layer
May 11 12:16:36 simon-Dell-T7400 dbus[841]: [system] Successfully activated service 'org.freedesktop.PackageKit'
May 11 12:16:36 simon-Dell-T7400 AptDaemon.PackageKit: INFO: Initializing PackageKit transaction
May 11 12:16:36 simon-Dell-T7400 AptDaemon.Worker: INFO: Simulating trans: /org/debian/apt/transaction/0516e323d8a64e68957c649bc240fbc3
May 11 12:16:36 simon-Dell-T7400 AptDaemon.Worker: INFO: Processing transaction /org/debian/apt/transaction/0516e323d8a64e68957c649bc240fbc3
May 11 12:16:37 simon-Dell-T7400 AptDaemon.PackageKit: INFO: Get updates()
May 11 12:16:38 simon-Dell-T7400 AptDaemon.Worker: INFO: Finished transaction /org/debian/apt/transaction/0516e323d8a64e68957c649bc240fbc3
May 11 12:16:51 simon-Dell-T7400 kernel: [ 5540.470950] NVRM: Xid (0000:02:00): 13, 0001 00000000 00005097 00001344 00004001 0000000d
May 11 12:17:01 simon-Dell-T7400 CRON[3772]: (root) CMD ( cd / && run-parts --report /etc/cron.hourly)
May 11 12:22:37 simon-Dell-T7400 AptDaemon: INFO: Quitting due to inactivity
May 11 12:22:37 simon-Dell-T7400 AptDaemon: INFO: Quitting was requested
May 11 12:37:00 simon-Dell-T7400 kernel: [ 6749.556313] Xorg[2935] general protection ip:7f30950fc6a9 sp:7fffe1a7f170 error:0 in nvidia_drv.so[7f309509b000+6e0000]
May 11 12:37:00 simon-Dell-T7400 gnome-session[3110]: Gdk-WARNING: gnome-session: Fatal IO error 11 (Resource temporarily unavailable) on X server :0.#012
May 11 12:37:00 simon-Dell-T7400 acpid: client 2935[0:0] has disconnected
May 11 12:37:00 simon-Dell-T7400 acpid: client 2935[0:0] has disconnected
May 11 12:37:00 simon-Dell-T7400 acpid: client connected from 3797[0:0]
May 11 12:37:00 simon-Dell-T7400 acpid: 1 client rule loaded
May 11 12:37:01 simon-Dell-T7400 acpid: client connected from 3797[0:0]
May 11 12:37:01 simon-Dell-T7400 acpid: 1 client rule loaded
May 11 12:37:01 simon-Dell-T7400 rtkit-daemon[1595]: Successfully made thread 3918 of process 3918 (n/a) owned by '104' high priority at nice level -11.
May 11 12:37:01 simon-Dell-T7400 rtkit-daemon[1595]: Supervising 1 threads of 1 processes of 1 users.
May 11 12:37:01 simon-Dell-T7400 rtkit-daemon[1595]: Successfully made thread 3920 of process 3918 (n/a) owned by '104' RT at priority 5.
May 11 12:37:01 simon-Dell-T7400 rtkit-daemon[1595]: Supervising 2 threads of 1 processes of 1 users.
May 11 12:37:02 simon-Dell-T7400 rtkit-daemon[1595]: Successfully made thread 3921 of process 3918 (n/a) owned by '104' RT at priority 5.
May 11 12:37:02 simon-Dell-T7400 rtkit-daemon[1595]: Supervising 3 threads of 1 processes of 1 users.
May 11 12:37:02 simon-Dell-T7400 rtkit-daemon[1595]: Successfully made thread 3922 of process 3918 (n/a) owned by '104' RT at priority 5.
May 11 12:37:02 simon-Dell-T7400 rtkit-daemon[1595]: Supervising 4 threads of 1 processes of 1 users.
May 11 12:37:02 simon-Dell-T7400 rtkit-daemon[1595]: Successfully made thread 3923 of process 3918 (n/a) owned by '104' RT at priority 5.
May 11 12:37:02 simon-Dell-T7400 rtkit-daemon[1595]: Supervising 5 threads of 1 processes of 1 users.
May 11 12:37:02 simon-Dell-T7400 rtkit-daemon[1595]: Successfully made thread 3926 of process 3926 (n/a) owned by '104' high priority at nice level -11.
May 11 12:37:02 simon-Dell-T7400 rtkit-daemon[1595]: Supervising 6 threads of 2 processes of 1 users.
May 11 12:37:02 simon-Dell-T7400 pulseaudio[3926]: [pulseaudio] pid.c: Daemon already running.
May 11 12:37:08 simon-Dell-T7400 rtkit-daemon[1595]: Successfully made thread 4068 of process 4068 (n/a) owned by '1000' high priority at nice level -11.
May 11 12:37:08 simon-Dell-T7400 rtkit-daemon[1595]: Supervising 6 threads of 2 processes of 2 users.
May 11 12:37:08 simon-Dell-T7400 pulseaudio[4068]: [pulseaudio] pid.c: Stale PID file, overwriting.
May 11 12:37:08 simon-Dell-T7400 rtkit-daemon[1595]: Successfully made thread 4090 of process 4068 (n/a) owned by '1000' RT at priority 5.
May 11 12:37:08 simon-Dell-T7400 rtkit-daemon[1595]: Supervising 7 threads of 2 processes of 2 users.
May 11 12:37:08 simon-Dell-T7400 rtkit-daemon[1595]: Successfully made thread 4097 of process 4068 (n/a) owned by '1000' RT at priority 5.
May 11 12:37:08 simon-Dell-T7400 rtkit-daemon[1595]: Supervising 8 threads of 2 processes of 2 users.
May 11 12:37:08 simon-Dell-T7400 rtkit-daemon[1595]: Successfully made thread 4152 of process 4068 (n/a) owned by '1000' RT at priority 5.