I've been using Linkit One boards for a while and found that many people ignore this simple but mandatory step: Updating the Firmware.
So here's a 1-minute screencast of how it's done using Mac OSX.
The process should be similar in Windows. For more information, refer to the official Mediatek Labs guides: https://labs.mediatek.com/site/global/developer_tools/mediatek_linkit/get-started/index.gsp
IMPORTANT: There's a switch in the board that reads either "UART" or "MS";
When you're done, switch the board back to "UART" mode and go to your Arduino IDE. You should see the Linkit Port:
You're now ready to code! Have fun.