MacBook Pro won't go past login screen Recovery/Ext boot won't work

Everytime I get the same, it gets stuck on the screen right after where the desktop should go up. Usually white screen, but also blue screen and also blue screen with black vertical lines. Running out of options...

Recovery mode won't work, external boot drive won't either. Always get stuck after the apple logo screen. Tried Internet Recovery, same result. When entering Target mode I can access the HD ok, so I made a backup in case. Hardware test mode works, tried both test modes, says everything is fine. Took it apart, removed on of the RAMs, tried both by themselves on both slots just because, again nothing. After some search I found that it could be a GPU issue, but shouldn't the hardware test pick it up? Any ideas?