DFRduino Mega2560 5v connectet to vin and 5v pins

On my DFRduino Mega2560 I have connected both the 5V and Vin pins together to 5V. Now my PC does not recognise it anymore, but as far as I have checked the integrated voltage regulator works (both 3.3V and 5V), the On LED lights up and on reset the L LED flashes.

So it seems like everything is still working except the USB.

Do you have any idea what could be broken and how it broke?