Did you install using 14.04.2 media? Then you're using the driver stack from 14.10. You could try using 'Option "AccelMethod" "uxa"' in xorg.conf (man intel), or update to vivid lts stack in trusty-proposed.
Did you install using 14.04.2 media? Then you're using the driver stack from 14.10. You could try using 'Option "AccelMethod" "uxa"' in xorg.conf (man intel), or update to vivid lts stack in trusty-proposed.