To shut down:
1. Bring up a terminal window with <Ctrl>+<Alt>+<t>
2. Then type:
type in your password at the prompt (the cursor will show nothing while you type, not even a string of ******, but it is still accepting your password). This will shut down the machine elegantly and immediately.
sudo shutdown -h now
If you cannot bring up a terminal with <Ctrl>+<Alt>+<t>, then try <Ctrl>+<Alt>+<F1>. This will switch you into a separate command line console. After logging in, typing the same command as above will also shut down elegantly.
Re: no desktop.
1. Run your system from a LiveCD. Tell us if this works.
2. Are you using Ubuntu, Kubuntu or Lubuntu?
3. Did you install as dual boot?
4. Have you already tried reinstalling from scratch?
5. If the same issue exists after reinstall, or you are set on chasing down the problem on your current install, then need the following info:
Open up a terminal as per above instructions and type:
Post results back to this thread.
cat /var/log/syslog | grep segfault