I have had the FLEX 6400 and 6300 for years and this is the first time I am having this problem after making thousands of contacts. It just started recently...When transmitting, I will hear the USB disconnection sound in the computer. The radio continues to transmit but on the next "over" the radio will switch into TX but there will be no RF transmitted. I tried the USB solution and expanded all of the Universal Serial Bus controllers to make sure Power Management was not turning them off to save energy. I also changed my Power Settings in Hardware and Sound which was another solution I found in this forum. All to no avail. I restart WSJT and it will work for one transmit and then go dead. All the time, I am hearing the USB disconnection sound in the computer when this happened. As stated by others, it seems that there is a virtual USB port being used here with the software. Of course, the FLEX radio is connected directly via ethernet cable to the computer. This is not a network connection. I would rather avoid swiping the drive and starting from scratch but I have been there and done that before. Does anyone have any suggestions?