Just replacing the USB board (or "versatile unit" as the documentation calls it) did not fix my USB. My first Phantom came with it not working, hobby store replaced it with no hassle, the replacement worked long enough for me to enable the IOC, manual mode, etc, but then also stopped working. Maybe their USB design has very poor ESD protection (protection against electrostatic shock). Everyone should take great care when connecting to the PC. Make sure you ground yourself by touching the PC chassis to discharge any static electricity before touching the USB connection. It may easily be something else, but given the fragility of the Phantom USB, if yours is working now, make sure you baby it.