I have an Uno, and I can play all I want with it, just using a USB cable.
Then I got two Nano clones, and they both show the same behavior:
When I connect it to the USB cable (which leads to my PC) it blinks a few times, then seemingly does nothing. I am also not able to connect to it via the Arduino IDE.
If I then connect an external power source to Vin and Gnd, it wakes up and blinks forever, and I am able to connect to it.
Is this just because I got a cheap clone? Or is this really the accepted / expected behavior?