I thought my wireless optical mouse needed a new battery. When I moved the LPC17 core I was programming the mouse stopped working completely. With a little investigation I realized the mouse worked fine with the core unplugged (USB power and connectivity). Eventually the fix was to replace a dirt-cheap USB cable with a decent, but not expensive, Belkin cable.
I tore into the cheap cable and found only a foil-wrap shield without a drain wire. The foil was not connected at the computer end of the cable. Well, the moral of the story is obvious. Spend a little more for reasonable quality. In the case of these two cables the difference in sheilding was obvious from the way the better cable kept its shape when coiled.