Hello. I'm trying to get rid of my Bumblebee set up and just use the NVIDIA card (or better yet, use NVIDIA-Prime, if possible). I followed the instructions here: https://wiki.debian.org/NvidiaGraphicsDrivers/Optimus, but when I restarted lightdm, the screen was black, and remained that way until I reverted all of the changes. Is there some step missing from these instructions?