Black Screen on Kali

I think I've just screwed up everything on my Kali .I wanted to install nvidia driver.
http://docs.kali.org/general-use/ins...-on-kali-linux

I've followed the whole documentation above, then rebooted .
But now , all I see is black screen.I doubt of something but I'm not really so sure about it.
I think the problem might be 2 GPU's on my laptop .
Because , when I type < lspci|grep-i vga > I see 2 GPU's listed . One is , Intel HD Graphics, the other is nvidia .
I have installed nvidia driver successfully but how can I solve this issue and get my GUI back :( ?

I can type ctrl+alt+F1 then log in , but really not sure what to type in :(

I want to be able to use nvidia , so CUDA but seems like there's no such a way on an Optimus laptop .

Thank you all for reading ... :)