MacOS – Does Macbook Pro have a hardware or software issue? (Constantly Stuck on White Screen)

My Macbook Pro Late 2011 (running on Sierra) has suddenly started having the white screen problem and I've tried the following:

• NVRAM, PRAM and SMC reset (could not get past loading bar after
  entering my user password)
• Running in Safe Mode (could not get past loading bar after entering
  my user password)
• Running in Single-User Mode (fsck shows no problem with the SSD
  drive, got white screen after "exit" command)
• Running in Verbose Mode (got white screen after I was in verbose mode
  or got white screen after "exit" command)
• Running in Target Disk Mode (connected with a thunderbolt cable, I
  was able to login to my account on the second Macbook by choosing the
  main Macbook's SSD from boot selection menu at the
  startup on the second Macbook. I copied everything on my main SSD to
  an external HDD, so erasing the drive would not be a problem. However, the
  second time I've tried this, I could not get past the loading bar after
  entering my user password – just like I couldn't on the main Macbook)
• Running in Target Disk Mode (this time as an external drive, on the second Macbook I got
  the error "macOS could not fix this hard drive, you can still access
  files but reformat it asap". So, I thought the SSD on the main Macbook has a problem and
  it was causing this problem!)

After this, I've erased the main SSD and tried to install a fresh macOS Sierra into the empty SSD. However, I got a white screen in the middle of the installation! (side note; I was installing from a bootable external HDD via USB).

After many tries and fails, somehow I was able to come to the final stages of installation (where you create a user name, password etc.). I entered the information and hit finish, then the computer just froze (the cursor and everything). I could not finish the installation on the main Macbook.

-Bear with me here-

I was not ready to give up, so I put the main Macbook into Target Disk Mode and I finished the installation on the second Macbook. Logged in, could see my fresh desktop.

I hoped it would work just as fine on the main Macbook, but now I cannot even see the user login screen. The only thing I can see is the Apple logo and the progress bar that never finishes loading (because it gets interrupted with a white screen, it fills 3/4 approximately).

So my question folks, does my Macbook Pro Late 2011 have a hardware or software issue? If it is hardware, what could it be? Keep in mind that I do not have anything plugged in or changed any hardware recently.

Thanks for reading, hoping for an answer.

Cheers & stay safe!

UPDATE: I've installed a fresh macos Sierra to an external HDD and plugged it in my main Macbook Pro, selected that drive using Option key and I still can't get past the loading bar with Apple logo (get white screen).