"unable to connect to X server: Connection refused" after setting up Git on Raspbian Buster

Hi,

I was working on my Raspberry PI 4 with Raspbian Buster
and today I installed and set up Git by these commands :

$ sudo apt-get install git-all
$ git config --global user.name <myname>
$ git config --global user.email <myemail>
$ git config --global core.editor vim

And then I turned off my RP, after that, Raspbian doesn't start with X11.
Whenever I try to execute startX, it doesn't start with some error messages like :

.....
xinit: giving up
xinit: unable to connect to X server: Connection refused
xinit: server error

Why does this kind of things happen and how can I restore my system?

Please somebody help me out.