Make sure your nvidia driver is properly installed

To make sure that the card is properly running within your system, you should run glxgears, it is a small openGL application that can only run properly if you have an openGL card installed :

# glxgears -info
Running synchronized to the vertical refresh.  The framerate should be
approximately the same as the monitor refresh rate.
GL_RENDERER   = GeForce GTX 750 Ti/PCIe/SSE2
GL_VERSION    = 4.6.0 NVIDIA 390.87
GL_VENDOR     = NVIDIA Corporation
GL_EXTENSIONS = GL_AMD_multi_draw_indirect [...]

if you do not see your card here, make sure all nouveau related components are uninstalled (driver, nouveau-xorg configurations…). You should use aptitude to see the dependencies.

Once nouveau is removed, you can install nvidia-xorg conf (search for nvidia with aptitude) and restart X (or reboot)

Make sure Nvidia Cuda toolkit is installed

Blender is using Cuda directive to render the scene, so you need Cuda toolkit to be installed otherwise Blender won’t see your card even if it is properly working.

So install cuda toolkit :

# aptitude install nvidia-cuda-toolkit

restart Blender once installed, and that’s it !