My screen shows black

@jaatmafia if the aforementioned diagnostics and solution does not work, you need to consider that this is a GPU issue. This series of laptop was plagued by the "chip flip" failure.

Your GPU processor is a flip chip design and the issue could be the solder bumps between the IC and the substrate. Sometimes a reflow with a heat gun may just accomplish a temporary repair. It is not a permanent fix, nor is it a sure thing either. It all depends on the individual logic board and the damage to the solder joints as well as the chip itself. A permanent fix would be a total reball. For a reball to be done, you will need the stencil, a rework machine as well as the proper reball temperature template, and a new processor, which by now is most likely no longer available. Yes, you do want to replace the thermal paste as well. Here is a very "quick and dirty" explanation of what causes most of the issues and it is pretty much the same for the YLOD, the XBox RROD as well as multiple others like HP and Apple.

It is not always a failure of the solder balls which connect the Flip Chip BGA package to the motherboard. It does happen and you can see why on here More commonly however is that the failure is due to the chip design itself.

As you can see the "bumps' are what actually connects the die to the substrate to make the chip complete. If these bumps fail the die does no longer make contact either he substrate and thus no contact with the circuit board. The chip has failed.

Here you can see the space where the bump has failed and no longer makes contact. We are talking microns of space here. So a bit of pressure on the top of the die potentially close the gap. Same with a reflow, it may allow some of material from the bump to reshape and starting to make contact again. The heating of cooling of the chip during use is what will eventually cause it to fail again.