remove gnome desktop

If GUI is troubling you, login through CUI(Ctrl+Alt+F1)

Check if "ppa-purge" package is installed or not.

Run

dpkg -l | grep ppa-purge

If it returns the value, "ppa-purge" is installed. If not, install it as follows;

sudo apt-get install ppa-purge

After that run the following commands;

sudo ppa-purge ppa:gnome3-team/gnome3-next
sudo ppa-purge ppa:gnome3-team/gnome3-staging
sudo ppa-purge ppa:gnome3-team/gnome3

sudo apt-get remove gnome-shell ubuntu-gnome-desktop

Reboot system and login through Unity.