Shimano Nexus 7 gear hub slips I need help on adjusting my Nexus 7 Shimano rear hub.

Today I tried to install a Shimano 7 gear shifter to change the gears on a Nexus 7 Shimano rear hub. Before installing, I lined up the red lines on the hub and I set the shifter to 4. 

Next I lined up the red lines even better by the adjusting-wheel near the shifter. 

The setup did work momentarily at one point. However, soon after the whole thing did not work anymore. 

The problem: When I pedal hard the rear gear slips and does not drive the back wheel anymore. It is the same for every gear. I tried every position of the adjusting-wheel. After more than two hours and no success, I gave up. 

Does anyone have a solution or the same problems? Is all the needed info here?
If I understand correctly you are trying to use a conventional 7 speed derailleur shifter on a Nexus hub. The Nexus hub does not use a linear cable pull ratio. The amount of cable pull required to shift is not the same from 1st gear to 2nd as required from 2nd to 3rd. A conventional 7 speed shifter pulls 2.9mm of cable between each gear. So you need to get a Nexus compatible shifter or risk hub damage due to improper adjustment.