As stated you must install the CH340 serial chip driver if you have a cheap Chinese knock off arduino that looks like this:
The chip in question is located under the crystal next to the usb port.
For me the only thing that worked was downloading the drivers from the Chinese website: CH341SER.ZIP - 南京沁恒微电子股份有限公司
And install as adminstorator! The files provided from the google drive did not work for me.