When you plug your dongle into the computer make sure it is showing up in the device manager of Windows (you should hear a sound when you plug it in) If it doesn't show up check you USB cable first, then check the dongle, does the red light come on? If it does then it is getting power over the USB line just not connecting. No red light = no power. While it is possible the USB module could go bad the most likely culprit is the 485 chip I would replace that first. Also if you have access to a PIC programmer check and make sure the pic is still programmed by doing a read and see if the resulting check sum match the wiki info.