So, the sollution is pretty simple. Remove R8556 R8558 for board 820-00840. These are SMBUS_SMC_1_S0_SDA / SCL ALS Lines. since this laptop will fail because of the broken LCD Cable, display replacement makes zero sense.
I believe this problem is caused by dead capacitors in the power circuit. It explains all syptoms. I tried two replacement cables and it did work on low mAh hard drive i used for tests in computer service nearby. When i came home and tried my own wd black, it did not even started. I think it could be fixed by capacitor replacement but thats really tricky thing to do as there is no schematics availible.