I am at my wit's end. I've spent 2 days (total time six hours) trying to reload drivers, reload software, switching between online and off line apps, and none of them will talk to my Arduino Uno chip. The port option remains greyed out no matter what I do/upload/reload. Unless there is assistance available in this forum, I am going back to Basic Stamps. Never once had an issue communicating with a Stamp.
Make sure the USB cable is completely plugged in to both the Uno and the PC.
You may have a damaged/defective or charge-only USB cable. Try a different cable.
Which operating system are you using?