I hate to admit this, even though I have worked with technology for more years than I care to admit, I didn’t know this simple technique for getting USB devices back in line. Shutdown your machine and then UNPLUG it!!
I had been struggling for a while with my USB devices- losing my external hard drives so they couldn’t be found anymore, having my external display stop working, any number of annoyances. I would grumble, and sometims scream and curse in frustration, finally give up, and reboot, and… nothing. Finally, one day I happened to enter in the right combination of words into Google and viola!! I found my answer. After you shut the laptop down, unplug the darn thing. Apparently, while plugged in there is still juice going to the mother board (the hardware brains of the computer) and it keeps track of the USB devices that way (not very well, I might add). In any event, if you unplug the computer, the mother board will “forget” about the devices and you can start over.
Well, it worked like a charm for me! I hope it works for you too- BEFORE you go out and buy a desktop with more USB ports like I did 
