Re: GLX problems after failed rollback attempt
Pretty messed up.
Mixing the nvidia (sh NVIDIA...run) and debian/ubuntu (apt-get) way of installing the driver traditionally results in mayhem. That includes different versions and installation paths for the kernel module and libglx libraries.
You should have de-installed 190.42 (NVIDA...run --uninstall or so) before going to 173. When going back to 190.42, get rid of all 173 packages by removing all nvidia packages apt-get has installed (includes libglx in 'nvidia-glx'), and then re-install the NVIDIA..run file again.
Regarding the original black-screen problem with 190.42: The Xorg.log of that failure could help here (possibly starting X with higher verbosity level). Alternatively, you could try 195.22, which is supposed to be better with newer GPUs.