USB Device Not Recognized. I had this problem after installing driver/software for SAMSUNG YP-F1 XB. Worked fine as memory stick previously. You name it, I tried it - all failed to cure problem.
Then I shut system down, unplugged it and shorted the L to the N on the plug, an old trick but worth a try. Power back on and start up - problem solved.
The SAMSUNG does not like being removed when powered up either - some devices don't seem to mind! So if you do this out of habit or just plain forget, this might just get your system reset.