drivers - Installing Nvidia Geforce on Ubuntu 14.10 & 14.04

I installed Nvidia Geforce GTX 850m driver from Nvidia official site on Ubuntu 14.10 & 14.04 and when restart laptop after installation process I get black screen I can't even access terminal
I don't know what's wrong with this driver ?

Any way to install the driver and work fine ?

If u get only black screen than try it.first start your ubuntu in nomodoset
here is solution open this link and follow step

My computer boots to a black screen, what options do I have to fix it?

here is simple step:-

when the grub menu appear press 'e' to edit button

then find quiet splash and delete this quiet splash

and type nomodeset and than press ctrl+x

you can install your graphics driver

but remeber your screen resoultion set 800x600

but dnt worry after your system reboot u can access your ubuntu in 800x600 resolution...

open your terminal and type

sudo add-apt-repository ppa:bumblebee/stable
sudo add-age-repository ppa:ubuntu-x-swat/x-updates
sudo apt-get-update
sudo apt-get install bumblebee bumblebee-nvidia linux-headers-generic