This has worked in my case: http://vxlabs.com/2015/02/05/solving-the-ubuntu-14-04-nvidia-346-nvidia-prime-black-screen-issue/
This has worked in my case: http:// vxlabs. com/2015/ 02/05/solving- the-ubuntu- 14-04-nvidia- 346-nvidia- prime-black- screen- issue/