After inserting the pen drive check disk management in the control panel.
Make sure the USB port works by inserting something else. If not, check the bios and motherboard cables. Delete the entries in Device Manager and let Windows recreate them on reboot.
Sometimes the motherboard needs to be “rebooted” also because something can go wrong, i.e. all your USB ports suddenly stop working. The small microprocessor on the motherboard will reload the drivers and your USB ports should be back to recognizing all devices!
So first turn off your computer using Shut Down or pressing the power button and then UNPLUG it from the wall outlet. Let it sit for about a minute and then plug it back in.
Hope this helps someone fix that pesky “USB device not recognized” Windows error!http://www.online-tech-tips.com/computer-tips/usb-device-not-recognized/