Ok... If there is a new kernel.

Very recent kernels, the build daemons that build for non-free aren't as "fast and furious". This means they are behind 99.9% of the time. Sometimes a week or more passes without it making it through the process without error requiring a manual tweak... as we know nVidia stuff is a bane to existence in the open source world... as noted by Linus Torvalds "eff you nVidia" rant a while ago.

This mean, that you then have a new kernel and new nvidia sources, but not any binary package available for install from the repositories.

We basically go through, requiring build packages:

module-assistant [options] COMMAND [ packages ]

I just use "m-a" which is an alias for "module-assistant", and I go through the menu system.

You've got to "update, prepare, get(package), build(package), install(package)"

And voila, I get my binary nVidia .deb for my kernel.

Restart my "display manager" (being LightDM currently) and whammo, it works again.

Of course, I have a supported Video card with the "nvidia-current" or just plain "nvidia", so YMMV on the older unsupported (by nVidia) nVidia video cards.