Does Nano not get sufficient power via USB? 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?
I have a few clones but have not seen this behaviour so I guess it could be one of three things (in order of most likely to least):


They have a fault related to taking power from the USB connector.
The USB lead is not able to supply enough power ie. it is cheap and extremely thin and cannot carry much current. Have you already tried other cables?
Your USB port cannot supply enough power. Given that the spec says 500mA from a USB 2 port, this seems unlikely unless the port is faulty. Have you tried other ports / another PC?