LG G3 completely dead

I had updated my phone recently to marshmallow, since then all was trouble !
It first started with the Sim not working until it has bricked, I hard bricked it and downloaded the kitkat and iy was completely working.
However, after I realized I cant bear using an old OS, i just let it to be upgraded again automatically, and it has been briked for ever.
I could easily get to the 9008 qualcomm mode but it doesnr work after that as it does go off in the middle of the soft brick with flashtool.
Now I cant get to the qualcomm mode any more as i think ive sorted the pins excessively or its a power problem.
Please help what should i do:
– What could be the problem for the brick?
– What are the different ways to short the shipset(ive tried 2 ways if there are more to try).
– How should i test whether the motherbiard was screwed for ever?