Nvidia GPU gives error 43 and I am unable to fix it. Which part is broken?

EDIT: My gtx 780m was dead and I upgraded to a 980m.

Let me start with telling the whole story of this situation.

I have a 4 years old GT70 2OD with an Nvidia GTX 780m gpu.
4 days ago, I left my pc with a game on main menu to get some meal.
When I came back, the pc was on lock screen and after I checked the windows event viewer I learned that it BSOD'd with the error "nvlddmkm.sys".
After that, I opened up my game again and after half an hour or so I got the same "nvlddmkm.sys" error once again. I gave it another try and got the same error one last time.

Googling the error I decided to reinstall my nvidia drivers.
I succeeded on reinstalling the drivers and after the compulsory restart I got my first error 43. (Windows has stopped this device because it has reported problems. (Code 43)")
When I try to open the nvidia control panel I get a "You are not currently using a display attached to an NVIDIA gpu." error.

What I have tried:

• - Reinstalled Nvidia and Intel GPU drivers in different orders more than 10 times. Tried using Display Driver Uninstaller many times too.
• - Reinstalled (clean, without any files left on C) windows 10 creators update and got the default drivers from windows update.
• - Removed the MXM gpu board from the motherboard and put it back.
• - Reinstalled (clean, without any files left on C) windows 8.1 using an iso and installed the supported drivers from the msi support page.
• - Flashed the gpu bios backup that I had using nvflash.
• - When I was planning to post on related forums about my problem, I noticed that the MSI Helpdesk application was unable to detect my EC firmware version and serial so I reflashed the latest EC firmware and did an EC reset (removed battery+cable for 5 mins).
  This brought back the EC version to the MSI helpdesk application but the serial number was still FFFFFFF.

With that last point, I am now suspicious that the problem might not be with the GPU after all.
If it was just a broken gpu, I was planning to get a GTX 980m and upgrade but the computer is able to detect the plugged in GPU as a 780m and not as a random PCI-E card.
But now that I don't know what is broken, I am unable to do anything as I don't want to trash a working GPU and my money.
What can I do about this?

Information:
MSI helpdesk output (bios & ec versions, installed programs etc.): https://pastebin.com/TdxPT4Jb
Screenshot album of gpu-z, device manager error 43 and "You are not currently..." error: http://imgur.com/a/GL6s8

Tomorrow when I'm back from work I'm planning to completely disassemble and reassemble the whole pc.
Maybe that will work. Hopefully.

 

This type of issue can be either GPU or motherboard. So if GPU is working but not the circuit on the MB then symptom will persist.

 

Thanks for the answer.
I decided to send it to msi support as I can't be sure which part is broken yet.
At worst I'll just pay the diagnostic money and get my notebook back to do the repair myself.