It's ugly: https://www.sugarsync.com/piv/D435904_81_8707554623
My guess is the monitor cable. But help is welcome: I don't wana take it apart. This is my first mac, never fixed any before. So I would thankful for a software problem.
ps.: Due to dammed design "flaws", I cannot just take the monitor and plug it into another machine, as I do with PC. T_T
Thanks for any help!