Unknown model of computer does not power off on shutdown

Thanks for taking the time to report this bug and helping to make Ubuntu better. Unfortunately we can't fix it, because your description doesn't yet have enough information.
Please include as attachments the following additional information, if you have not already done so (please pay attention to lspci's additional options), as required by the Ubuntu Kernel Team:
1. Please include the output of the command 'uname -a' in your next response. It should be one, long line of text which includes the exact kernel version you're running, as well as the CPU architecture.
2. Please run the command 'dmesg > dmesg.log' and attach the resulting file 'dmesg.log' to this bug report.
3. Please run the command 'sudo lspci -vvnn > lspci-vvnn.log' and attach the resulting file 'lspci-vvnn.log' to this bug report.
4. Please run the command 'sudo dmidecode > dmidecode.log' and attach the resulting file 'dmidecode.log' to this bug report.
For your reference, the full description of procedures for kernel-related bug reports is available at https://wiki.ubuntu.com/KernelTeamBugPolicies . Thanks in advance!

I've had similar things happen to me.

1. When the screen is black, can you still see the mouse arrow?
2. Can you switch to the console? To see if you can, use Ctl-Alt-F3 to bring up tty3.
3. If you can get to a console, log in and issue the shutdown command, like this:

ubuntu login: yourusername
Password: yourpassword <-- Nothing will show here when you are typing yourpassword. Just trust your typing and then hit enter.
<the boilerplate yada-yada-yada>
yourusername@ubutntu# sudo shutdown -hP now
Password: yourpassword

4. If you cannot get to a console, does the machine respond to a Ctl-Alt-Del reboot (The infamous "Three Finger Salute")?

5. If the machine does not reboot after Ctl-Alt-Del, does your keyboard NumLock LED light respond when you hit the NumLock key?

6. Post as an attachment /var/log/Xorg.0.log.

7. Post the RELEVANT portions of /var/log/syslog. The relevant portions are those lines with the timestamp of around the time you tried to shutdown. DON'T post the entire syslog, which would probably be an enormous amount of irrelevant information. (Unless your system just reloaded the logs.)

8. Is this a Dell computer? I have several Dells, and they all have weird hardware issues. I've figured out solutions for all of them, but they are strange until you get them figured out.

Post back with the answers. It will help troubleshoot where the problem is.

Happy Trails,

Loye Young
http://www.iycc.biz
Laredo, Texas

We are closing this bug report as it lacks the information, described in the previous comments, we need to investigate the problem further. However, please reopen it if you can give us the missing information and feel free to submit bug reports in the future.