I am using Ubuntu 14.04. I have big issues with the Unity desktop. I installed then uninstalled gnome-shell (using "apt-get autoremove --purge gnome-shell"). Since then, my desktop has no background and no icons. Plus, and this is the bothering part, unity is very unstable. On startup, there is a huge use of memory, much more than before. Sometimes, I also cannot minimize a window without having the desktop freezing and having to kill the process in question with tty1. I have tried to use :

apt-get autoremove --purge ubuntu-desktop
apt-get install ubuntu-desktop

But it does not change a thing. I tried to update my video drivers but it is still the same.

How can I reinstall the unity desktop thoroughly (obviously, something in its install is broken) ?

If it is not possible, is it safe that I create a new partition on my disk where I will put my files and reinstall Ubuntu on the old partition (I do have a USB install of Ubuntu 14.04 but not enough space to save my files on it) ?