I have tried shutting down and restarting from the desktop icon. Each time, the computer hangs at a blank screen and never shuts down. The fan starts whirring.

Then, I tried shutting down from the terminal to see what was causing the problem, and this is what I get:

wait-for-state stop/waiting
Enabling radio: wifi.
Applying power save settings...done 
*Stopping rsync daemon rsync  [OK]
*speech-dispatcher disabled; edit /etc/default/speech-dispatcher
*Asking all remaining processes to terminate...  [OK]
*All processes ended within 1 seconds... [OK]
ModemManager [1295]: <warn> Could not acquire the 'org.freedesktop.ModemManager1' service name
ModemManager [1295]: <info> ModemManager is shut down
*Deactivating swap...
*Unmounting local filesystems
*Will now halt

After that, it gets hung up and the fan on the computer starts whirring.

Please help! Thanks in advance.

closed as off-topic by Daniel Foré, John Guerreiro, Lewis Goddard Sep 6 '15 at 20:42

This question appears to be off-topic. The users who voted to close gave this specific reason:

If this question can be reworded to fit the rules in the help center, please edit the question.