Make sure the PC’s operating system version is compatible with the USB interface. If you are using the USB interface in Class 2 mode with a Windows PC, you must load the dCS USB Class 2 driver first. USB Class 2 with a Mac requires OSX 10.6.3 or later. Try connecting to a different USB port on the PC or resetting the USB port. USB Class 1 mode should work with almost any PC with USB 2.0 interfaces so try switching the dCS device between Class 1 and 2 mode.