Make sure you are using a Null modem cable
Are you using a USB to serial converter?, if so you will need to install a compatible driver. You could try
this one or search for the prolific driver.
once you have installed the driver,
With your USB to Serial adapter connected to your computer, Null modem, and box.
1> Type in the search function in your start menu "device manager", then open it up
2> Expand Ports (COM & LPT) by pressing the + sign next to it
3> Double click "Prolific USB-to-Serial Comm port
4> Click port settings tab
5> Leave the default settings and select the Advanced tab
6> Set COM port to COM1 (PRESS OK)
7> REBOOT COMP
Then flash the box as per tutorial,
Only when above is done plug your RJ45 ethernet connector in from your router into the back of your box (peel the big black square sticker of the back to reveal it if you have not already)
Then you should be done.