If your Digilent or Xilinx USB cable is not working in Vivado, please follow the instructions below to check if it is installed properly.
Run the following command :
Check if the following two files are present:
If the files above are not present, run the installer from the following directory:
<YOUR_XILINX_INSTALL>/data/xicom/cable_drivers/<lin64 or lin32>/install_drivers/install_drivers
Note: It is important to have the JTAG cable unplugged while you perform the installation.