Dual-screen, nVidia no GUI

Good evening,

A friend told me such good things about Kali that i installed the last version today by imaging the amd64 iso file on my USB key and everything went perfect (a little bit confusing, coming from ubuntu, but still works !).

But even if the OS is (seemingly) OK, my hardware is not.

I have two screens plugged via DVI on my nVidia GTX 970 and here's the problem :
- If i unplug monitor 2, monitor 1 is the one and only monitor, everything is ok in that state (and i'm writing this post in that state)

- But if i plug monitor 2, monitor 1 seems to be the "second" monitor and monitor 2 (which was unplugged in state 1) takes the main. In GUI (ctrl+alt+f7) the old main monitor only displays the wallpaper while the "new" main monitor (the one which was unplugged) is completely black. If i switch to any terminal, the two monitors will display the same thing at the same time (and i can write shell commands in that case). But if i switch back to GUI via ctrl+alt+f7, monitor 1 (apparently the second monitor in that state) displays the same wallpaper BUT monitor 2 (apparently the new main monitor) freezes in the terminal and i can hoover my mouse's pointer over it like it was a GUI window ...

I looked up on the net and found that updating nvidia drivers might solve it. So i followed the official kali documentation about updating nvidia drivers.
After the "reboot" command, it did not display the "login" window (after the passphrase) but the sadly well-known "Oh No ! Something went wrong !"

I panicked (yeah, maturity ...) and i purged the nvidia drivers, putting the system back to "normal" but it did not solved my dual-screen problem.

And now, as before :
- One screen ? No problem !
- Two screens ? The main screen is now the second and the second is the main but does not display any GUI information

Never had this problem before but i'm still a very-beginner in Kali