Dell XPS 13 9333 (CID: 201309-14238) seems to have the same issue on 12.04.5.
Would you please try to re-install
libegl1-mesa-lts-trusty and ubuntu-desktop
and see whether the system goes back to 3D mode?
Please note the sequence is importance, libegl1-mesa-lts-trusty first and then ubuntu-desktop.
Dell XPS 13 9333 (CID: 201309-14238) seems to have the same issue on 12.04.5.
Would you please try to re-install
libegl1- mesa-lts- trusty
and
ubuntu-desktop
and see whether the system goes back to 3D mode?
Please note the sequence is importance, libegl1- mesa-lts- trusty first and then ubuntu-desktop.