Comment 8 for bug 990539

My apologies. You should remove nvidia-173. I was not aware of this bug: https://bugs.launchpad.net/ubuntu/+source/nvidia-graphics-drivers-173/+bug/948053

It looks like you're limited to open-source nouveau driver on Precise unless Nvidia decides to update their legacy driver for compatibility with later Xserver. If you demand nvidia binary driver, you'll either have to use an older version of Ubuntu or hack in the old Xserver to precise as suggested in that bug report (that's not recommended, but if you're adventurous...).