Anet A8 board USB broken?
I have this printer and used this board many times over USB.
The genuine Arduino boards use the FTDI FT232RL to convert USB signals to UART signals.
The problem with these Arduino based clone boards is that they do not use the FTDI chips as these are too expensive. These boards use a CH340G chip which is a Chinese clone which requires a specific driver to be installed before you can communicate with the board:

Image shows a close-up of the CH340G chipset on the Anet A8 controller board.
When you bought the printer, the SD-card contained the driver that you need to install on your OS. I remember that this driver was for the Windows OS. However, you can download the driver for many platforms (Windows, Mac and Linux) directly from the manufacturer.