USB or ethernet?
Shielded ethernet cable?
i have been networking pc's since token ring (before Novell)
i don't think i have ever used a shielded cable (at least not knowingly)
but, i am on the edge of my seat waiting for his answers.
i would disable all power management, but them start looking at the firmware, etc
if it is actually as consistent as he says, it might be worth resetting everything to default and starting over
AS YOU SAID
USB OR ETHERNET?
IF USB HOW LONG IS THE CABLE?
no hub or concentrator?