I have two Ubuntu Software Centers, one can be opened, another one can't

Recently my Ubuntu Software Center could not be opened(it opens showing nothing and exit automatically). I therefore ran the command sudo apt-get remove software-center to remove the Ubuntu Software Center. then I use sudo apt-get install software-center to reinstall it.

Now I have two Ubuntu software Centers; one is called "Ubuntu Software"(default broken one), another is called "Ubuntu Software Center"(the current working one).

The problem I have is that whenever I want to download something not in the Software Center, if I open the .deb file, the broken one opens it, and closes very quickly. Basically I can't download anything outside the Ubuntu Software Center for that reason.

My current Ubuntu version is Ubuntu 16.04LTS.

In 16.04, Ubuntu Software Center (ubuntu-software-center) was replaced by Software Install (gnome-software, or simply "Software" in Dash).

Most likely you had some left overs after upgrading from 14.04to 16.04. Subsequently, you reinstalled the old Ubuntu Software Center, while the newer gnome-software was also installed.

What to do

Since we do not know for sure what exactly happened and why, do the following:

1. Run the command

    sudo apt-get --purge remove software-center
   

2. Look into both ~/.local/share/applications and /usr/share/applications if you find any left-over .desktop files, named ubuntu-software-center.desktop, remove them if so.

3. Run

    sudo apt-get install gnome-software
   

After that, log out and back in to make sure, and gnome-software ("Software" in Dash) should be the only one.