CUDA rendering in Ubuntu 14.04

I am running a laptop with 2 GTX 980M cards. I do a lot of work with Blender 3D, and am trying to figure out how to install the cuda toolkit so I can render on the GPUs instead of the CPU. Every time I install the cuda toolkit, I am unable to do anything after I restart my system due to major stretching of the screen. I am currently running the GPUs using the latest 346 drivers with no problems, but am unable to use the gpus for rendering in Blender. Other than that, the GPUs are working fine for games, external monitors, and everything else. Does anyone have any advice on how to best resolve this?

By the way, here are my system specs in case you need to know them:

Sager 9377

17.3 inch 1920x1080 display

Intel i7 4940MX 3.1 Ghz CPU with hyperthreading

2x (SLI) Nvidia GTX 980M GPUs

32 GB Kingston RAM @ 1600 Mhz

2X Samsung Evo 840 SSDs (one for my OS and one for file storage)

Again, everything works fine, but I am unable to render using the GPUs in Blender 3D…

Thank you

but I am unable to render using the GPUs in Blender 3D…
I’m not clear about your issue. please share reproduction steps and log file by running script as root user?