Hello Scott,
If you're using the standard Microsoft-supplied driver for it, try using M-Audio's driver instead:
http://www.m-audio.com/index.php?do=support&tab=driver&serie_ID=4&PID=d69930bdc00ec73eb423226e8c8130ba&OS=x107#tabs
Also perhaps try attached the MIDISPORT to each possible USB interface (exit Hauptwerk before disconnecting/reconnecting it), and disconnecting any other USB devices that aren't strictly necessary.
If that fails you might need to try contacting M-Audio for support (perhaps it's a motherboard or BIOS issue for which they might have suggestions).
Hope that helps.