Hello,
I my drawing, actualy the Leds are ledstrips with risitors on it. I don't think this is the issue, because when i use the USB from my pc it's working fine. This i use the pc for powering the Arduino Nano and a power adaptor 12v foor the ledstrips via Vin port.
When i put a powerconverter from 12v (same adapter) to 5v and power the USB port with this on the board it doen not work. When u use my phone charger (USB output) and connect this to the USB port it is working also fine.
Edward