Ubuntu doesn't shutdown properly

This is a known issue - Bug #274995 The solution that works for most people is: Open the terminal and type :

sudo gedit /etc/init.d/alsa-utils
This  will open alsa-utils with Gedit, now find the instruction "stop)"
arount the line 353 . Below this instruction you should add these
two instructions:

 

ifconfig wlan0 down
ifconfig eth0 down 

so, the file should be this way :

stop)

ifconfig wlan0 down

ifconfig eth0 down

EXITSTATUS=0

 Save the file, close the terminal, and restart Ubuntu.

And is done.