Ubuntu won't shutdown

I wanted to report a bug but if I understand it right, somehow I cannot do that in my case...

My computer does not want to power off 70% of the time. Sometimes it successfully turns off, but mostly I just se Ubuntu logo with those little dots below it (progress bar), and everything freezes. Sometimes I also see the output, like this:

The system is going down for halt now
* Stopping TiMidity++ ALSA MIDI Emulation...
hecking for running unattended-upgrades:
* Stopping UPnP devices daemon minissdpd
minissdpd[1194]: received signal 15, good bye
speech-dispatcher disabled; edit /etc/default/speech-dispatcher
* Stopping VirtualBox kernel modules

I posted this two questions on askubuntu... but got no help:

http://askubuntu.com/questions/210959/ubuntu-wont-shutdown-virtualbox-kernel-modules

http://askubuntu.com/questions/210967/how-to-report-a-system-bug

Please help!