I have the same exact problem, same computer model. I believe it's ACPI related.
Linux 3.2.0-29-generic #46-Ubuntu SMP Fri Jul 27 17:03:23 UTC 2012 x86_64 x86_64 x86_64 GNU/Linux Description: Ubuntu 12.04.1 LTS Release: 12.04 -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1010981 Title: Computer does not power off when attempting to shut down by any route. To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1010981/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs