I am experiencing the same issue with exactly the same symptoms using Ubuntu 11.04 x64. I would add that the crash/reboot occurs roughly 40 seconds after doing seemingly anything other than re-launching an Ubuntu 11.04 based OS, including live CDs of other unrelated distros.
If the reboot occurs after launching Windows 7, the only record in the event viewer is a log of an unexpected shutdown.
I am experiencing the same issue with exactly the same symptoms using Ubuntu 11.04 x64. I would add that the crash/reboot occurs roughly 40 seconds after doing seemingly anything other than re-launching an Ubuntu 11.04 based OS, including live CDs of other unrelated distros.
If the reboot occurs after launching Windows 7, the only record in the event viewer is a log of an unexpected shutdown.