Asus Z53T doesn't starts properly anymore / Connect screen to G73JH

The Z53T behaves weird, it still seems to "boot" because the keyboard lights blink and the DVD drive makes the start noise but no picture appears on the internal or an external screen. The HDD lamp blinks for a sec short then long, no HDD is installed though. It doesn't change the behavior even if I remove the RAM. The screen goes from semi-dark to dark "black" when I turn it on, battery is loading fine and it also runs on battery, keys like caps lock are working (LED turns on/off).

PCIe POST card doesn't seems to work, only shows 0. and RST LED doesn't turns on.

Can I connect the Z53T screen to an ASUS G73JH btw? I would like to see if I can still sell it as working.

 

Small Update:

Managed to get it at least sometimes booting with graphics by warming up the GPU a bit with a hair dryer, then it does start every 2nd/3rd try~

So I'm pretty sure that it is the GPU, any suggestions for a fix apart of a new mainboard?

Screen, keyboard, touchpad, wifi, cpu, ram... works just fine. Once it starts with gpu the gpu works fine too, but thats sadly not always the case.

 

Nobody has any idea? Would like to avoid reballing the GPU :/