Now it is possible to remove the mother board. Please take this with a pinch of salt. I have only done this procedure once and don't know if there are any other screws left. So do the removal (sliding the board from left to right) carefully and if you notice some resistance double check for any screws.

As last step you can remove the fan and heat sink assembly fomr the mother board by unscrewing the 4 screws around the processor (metalic X shaped structure).

I hope that this helps someone. In my case I missed a guide like this to work on such complicated assembly.

Also I fixed the video problem using a heat gun on the envidia chip area as recommended in various links around. And finally placed a 5c coing between the envidia chip and the heat spreader, as I could not find any thick copper piece to be used as interface. The original blue rubber piece I found in the laptop wasn't in my view very effective.