Start Mathematica 10.3 in a Linux Computer?

We installed Mathematica 10.3 in a Linux Computer (ubuntu 12.04.5 LTS). It worked well several weeks and now it doesn’t start anymore. The error messages that we get are:

libGL error: failed to load driver: nouveau
libGL error: Try again with LIBGL_DEBUG=verbose for more details.

LinkConnect::linkc: -- Message text not found -- (LinkObject[ngdrk_shm, 3, 1])

Can someone give me some clues?