Thanos, not to point fingers or anything, but it sounds like to me long ago somebody had dropped your Mac and then tried to put it back on the desk and pretend things are OK. There is no way there should be damage on a video card as you describe unless somebody dropped something on it. And if so, what about the board itself?  If you get a new video card, try it on another slot than the one you have this first one on.

Can you post pics of the video card and logic board?