no link from Nano to PC

my Nano is integrated in a test setup for a long time, and it works well. Now I wanted to change the software on it. But when I connect the USB cable to the PC (Win 7) the serial port for it is not available. There is a choice of several serial ports, but not the one for the Nano.

Working with a Teensy 3.2 is ok. The serial port for it is detected. But after setting "Nano" in the Tools menue the serial port is not available. Plugging in the USB cable produces a sound on the PC as if the driver was detected, but it is not.

What can I do?

If the serial port does not work, you may be able to write the firmware with an ISP programmer, via the SPI port, or with a high voltage programmer if the ISP programmer does not recognize Atmega.

Is your board original? Which converter chip is in it? CH340 or FTDI?

I have had problems with low quality USB cable. The USB port can't provide much power either.