Ubuntu – Changing Nvidia Driver black screen

I searched everyone online for solution, but it is still not working.

At first I changed the Nvidia driver to use the propriety driver from the additional tab, twice, and it shows black screen which cause me to reinstall.

And then I learnt about the alt+ctrl+f1 to show command prompt.

When I tested Dota 2 in Ubuntu with nouveau driver, there is some lagging. And when I tried it in my Linux Mint, it works smoothly. My mint is using propriety driver.

So I decided to try to change it again on my Ubuntu. And Voila! Blackscreen ?
Seriously such a popular distro can have so many bugs? For example like suspending and not waking up? I could just change the driver in Additional Driver tab in Mint without problem but not Ubuntu?

So I tried many times purging it, installing dkms, downloading drivers from Nvidia sites, all sort of method.
Sometimes it shows black screen, sometimes login loop, sometimes logged in but no Unity, but I can right click open terminal and use the terminal though.

Seriously anyone got a proper solution for this? I updated and installed everything in my Ubuntu properly already I do not hope for a need to reinstall.
Thanks.

I'm Using Ubuntu 15.04

Nvidia GeForce GTX 860X

Intel i7-4720HQ with graphical in it

prime-select query shows

nvidia

xorg.conf file is default, not changed when booted up.

Actually I did try to change back to nouveau but it does not load Unity, probably because I'm using Compiz? But now I'm trying to get Nvidia driver to work!

EDIT : Now my Nvidia version is 346, from default repository. Still black screen

EDIT: I successfully changed back to nouveau and enable Unity through CCSM. Nvidia drivers are not working at all!