I have a K520 Logitech keyboard & paired mouse. The USB unifying device, slowly went bad and the computer system warned about a USB device that was over current, and to disconnect it, and the computer warned that it would shut off in 10 seconds. A good keyboard & mouse, and now it is worthless unless I can pair up a USB unifying device with it. The unifying device completely shorted out and now does not install in the USB connector. The cost of a single channel unifying device is about $ 8 dollars on ebay. The is Logitech UNIFYING SOFTWARE that can be downloaded, to try to pair up with the keyboard & mouse or use the $26.00 6 channel USB unifying device. This would only be seen with a software driver. Is this the only fix that can be done? I hate to throw out good quality keyboards and mice, if they cannot have a USB unifying device paired.