no faulty wires, no shorts. I've built two computers with the same issues now. The problem seems to happen on pretty much all USB ports.
I also have a problem with my mouse doing this, and I once solved the problem by plugging the USB key on to my G15keyboard's USB ports. But now I'm not using that keyboard anymore. The funny thing is that I once had the same problem with a PS2 mouse that I tried for a week.