Try going to Device Manager - right click on my computer and select MANAGE. Then Select Device manager on the list on the left
At this point make sure your USB that isnt working is plugged in.
There should be one device shownd as "? Unknown Device". In Yellow Font
Click this one, and select download driver.
Select the (Automatic Option)
I have had this problem on XP since reformatting. And this is the only way I have been able to solve this problem.