I saw, that when I press 0 and then for example 8 the cursor moves up, when I press 4 the cursor moves left, when I press 6 the cursor moves right and when I press 2 the cursor moves down.
This was the key piece of info. Go to System Preferences, Universal Access, Mouse, and turn off Mouse Keys. Mouse Keys is for people with disabilities and want to use the keyboard to control the cursor.
When I press a key on the Numpad, then the computer stops reacting on the mouse...Mouse and keyboard are both USB and, I tried another keyboard and another mouse. I just tried another port, but nothing works.
Mouse Keys should not have disabled your mouse. (It did not on mine.) If you mouse still does not work when Mouse Keys are on, when I said to try different USB ports, you would have also wanted to try plugging the mouse directly into the computer rather than into the keyboard. It is possible that both your keyboards have bad USB ports, or both mice are doing something funky like drawing too much power. In any case, continued troubleshooting is more for academic knowledge. So if you don't need Mouse Keys, turn it off and you should be good to go.
