ok, I connected the pins back to the arduino so they have a ground connection.
So from sensor to arduino:
Vin to 5V
GND to GND
RX to D6
TX to D7
with that connections, the arduino does not connect to my pc anymore. It is blinking but windows shows an error message that it cannot connect to the device. So I cant even upload the software. It is so frustrating. As soon as I remove the pins, the arduino connects to my PC again. I changed all the cables for new ones, still doesnt work. I took my old laptop, installed arduino and everything works and I can upload software, but as soon as I connect the pins of the sensor to the arduino it does not connect anymore. So same problem, it does not seem to be my PC. I also tried to connect it without pins, wait until windows and the software notices the device, then connect the pins of the sensor and upload the software, but that doesnt work neighter... how is that possible... how am I doing everything wrong.
Do you perhaps have a source of information or a book recommendation so I can get a little better with all this?