I had a similar issue with my HA-1. The USB input stopped working when I powered it on one day. I tried other inputs like S/PDIF coax and that worked fine. I had to return it for repairs, because nothing I did could get that USB port working. Also, when connected the now broken USB transceiver on the HA-1 was causing other USB devices (e.g., hard drives) to periodically disconnect. OPPO was great at helping me troubleshoot and take care of the issue, so kudos to them!
I have a feeling that either these units are very static sensitive or at least more so than all of my other USB devices (pure speculation on my part, since I don't know what kind of grounding or other static protection the USB port on the HA-1 offers) or there may be an infrequent USB transceiver issue (even wilder speculation on my part). In any case, mine is now connected through a powered USB hub to offer some static isolation from my PC and more importantly my fingers.
If anybody is looking for a hub that will work with the HA-1, this one does (
http://www.amazon.com/gp/product/B00DQFGH80/ref=oh_aui_detailpage_o04_s00?ie=UTF8&psc=1) for the low price of $19, as long as you plug it into a USB 2 port on your PC/MAC. It offers an extra level of security against static with the dry winter season, and its accompanying static shocks from everything you touch, on its way. If you get another USB hub, make sure that it is powered or you will not be getting decent static protection.
To confirm that you have a USB transceiver issue, try a different cable and more importantly try the unit with another computer if you have one just to rule out a problem with the PC/MAC that is sending the signal. Other than that, give their support a call.