Thanks MarkF48 , PJD and Eileen.Yes, the incident is definitely related to the USB. I had a USB Hub plugged in.My USB Hub has 4 switches on it. I think sometimes I am a bit impatient switching off one thumb drive in the Hub, and switching on another thumb drive. Fortunately, i have not had to power off, or reset my keyboard. I have made a promise to myself that in future I will slow down. Computers these days, respond so quickly,that I have grown to expect everything to happen instantaneously, and, maybe like us, they need a moment to gather their thoughts, and regroup.