Port not showing up indicates missing drivers, a bad USB cable, or damaged hardware.
Is the board an official one, or does it use a different USB-serial chip? Only drivers for the FT232RL (used in official nano) and Atmega 16u2/8u2 w/arduino usb serial f/w are included.
If you're using one of the clones with CH340G or CP2102, you must download and install the drivers separately - find the name of the serial adapter (look at part number on the black IC near the USB port) and google the part number, your operating system, and the word "drivers"