My first problem was that playing videos made everything freeze - totem was using almost all my cpu power. To solve this I installed nvidia drivers with
sudo apt-get install nvidia-###
Where ### was a number I found using http://www.nvidia.com/Download/index.aspx (for my card Geforce 630M).
This seemed to work. Video playing no longer froze my laptop (which is an Acer Aspire V3-571g if it matters). However, when I connected a second monitor I got some issues. Half of the second screen would be "cut off", only showing black. Entering nvidia-settings only showed the laptop screen
To solve this I found various questions and forum threads suggesting to do install nvidia-current instead. I did that, and ever since the GUI hasn't worked. I've tried things like
sudo apt-get purge nvidia*
and I've tried removing that /etc/X11/xorg.conf file - nothing has worked so far.
Any suggestions on what I can do?
Edit: I'm getting "Unable to connect to X server" now, when I go into terminal with ctrl+alt+F1.
UPDATE: I didn't manage to solve the problem, and in the end I just reinstalled Ubuntu.