Mac Issues ["-'_'- " ]

My 2012 Macbook Pro (the one without the bar; 13.3 inch) has been having some real bad issues. The software of this Mac is on Mac OS X El Capitan. Everytime I turn on my Mac the screen is always on the login screen with a white-greyish background and my user and the guest user option. Once I log in to my user, it shows a centered greyish apple logo and a white-greyish background with a bar underneath loading up. About halfway through of the bar loading, my Mac flashes black highlighted white letters starting from the top left corner of the screen down for about 2 seconds and then it automatically blacks out and restarts. Then a message saying "your macbook has restarted because of a problem" pops up with multiple different translations of that message and it tells me to wait. After that, it goes back to the same white-greyish screen the main user and guest user.

I have searched up about this a couple of times on the internet, but I am not really sure if these were the right solutions. I have gone into the Utility screen and erased the disk "Macintosh HD" and creating a new disk. And then I have gone to the option to reinstall the software, Mac OS X El Capitan, and it worked the first time. I had setup the mac after reinstalling the software and it was perfectly fine. I then went into the apple store and decided to upgrade the software. It then transitioned me into another problem. The Mac restarted and launched the same screen with the apple logo and the bar loading. The Mac then shutted down on its own. I turned it back on and the screen with bar came out again and this time it flashed the black letters and then it restarted and showed me the message. It then took me back to the login screen with the users.

I then went into the Utility screen again and did the same process as the last time it had worked. This time it took me hours to go through this process. I had finally now gotten into setting up the Mac. I am currently on the Welcome Screen of the setup where you pick your country with the maps and the drop down menu. Usually there is a back and continue button on the bottom of that window, but the buttons have no outline nor the blue color. Only the word back and continue are there, both unable to be selected. Now I seemed to be stuck on this screen.

Please help me! What do I do! I need this computer for school ASAP!!

Anyone have any solutions?? PLEASE? What could be the problem???