Computer will not shut down since update

Hi
Since avast has installed the most recent update (7.0.1456) my computer will no longer shut down - i am running Windows XP and thecomputer shuts down as far as the blue screen with ‘logging off’ in the centre of the screen but it will not complete the shut down which means I am having to hold power button to turn off then select start windows normally. I have restored to point prior to update and this resolves problem and then as soon as i run update it comes back - I have not loaded any other new software or programs.
I am not a computer wizz and I am a bit stuck !
thanks

System restore can have its issues with avast!
I suggest an installation from scratch:

  1. Download the latest version of avast! Uninstall Utility and save it.
  2. Download the latest avast! version and save it.
  3. (Optional) If you want, save your avast! settings for later restoration (Settings > Maintenance > Back up).
  4. Uninstall avast from Control Panel (if possible). If, for any reason, you can’t run it, try booting in Safe Mode and doing it from there. Anyway, boot after that.
  5. Run the avast! Uninstall Utility saved on 1 in Safe Mode. Boot after you’ve run it. Repeat this for any major avast! version you have ever installed/upgraded in your computer.
  6. Install avast! using the setup saved on 2. Boot.
  7. Register your free copy or add the license key for Pro. Or even upgrade your key from old versions.
  8. Check and post the results. If, for any reason, you did not solve, try doing the step 3 in Safe Mode anyway.