I want not open the display, yet (but if all other ways end...)
Ok, the ribbon cable is original (and yes, it´s about 10 till 15 years old). There are some instabilities on the display if I move it (but i can move it around and around, the "vertical problem" laughs at me

).
I discrimped an old serial port connector (´cause its 2x5 pin connector) and recrimped it on another old IDE ribbon cable. I will replace the original ribbon by this one and then I will check the LCD drive supply voltage (pin4 vs pin5)
Hmm, ok, I will open the computer again follow the way of the display-wires.
Why do I try to ... reactivate this computer? It was the first one, I bought!
What will I do with it, now? good question...
Maybe, I´ll try to use it as a display controller board (for it´s own display)
Data transferred by serial and/or parallel U(S)ART and all graphics and effects could be calculated by the laptops processor
But as far as the display does not work correctly...