I installed Ubuntu 14.04 on a computer with a NVIDIA GTX 590 graphics card. A few minutes after logging into Unity, the entire computer would freeze. Nothing would work, not Unity, not the mouse or keyboard and not even the Ctrl-Alt-1 terminal! This would repeat every time I powered off and powered on the computer.
/var/log/syslog I noticed that the last error message usually involved nouveau complaining that it could not read some memory address or failed on reading a memory address. This gave me a clue that the graphics driver was not working with this particular graphics card for some reason.
I looked for the latest NVIDIA driver in the Ubuntu repositories, named
xyz is the largest number you can find there and installed it. For example:
$ sudo apt-get update $ sudo apt install nvidia-331
I restarted the computer and Ubuntu worked fine after this. This is one of those rare instances where a NVIDIA driver prevented a crash, rather than cause one! ;-)