Nano CH340 power problem

Hi,

I use arduino nano (megaAVR - ATMEL ATMEGA328P AU) to control my led light.

I use power supply from standard smartphone to power up the leds and I use simple software on windows 10 to control it.
When I connect arduino nano to PC firstly and then power supply all works very well. But... when I firstly connect power supply and then to PC I get "no response" from arduino... Why? Anyone can help me?