Wow. Thanks guys. I will try your instructions ptillisch. Just to add to the confusion since my last post: yesterday my PC slowed to a crawl and I could not get IDE going at all. One of many things I tried was to delete temp files etc. but my PC was so slow that was agonizing. So I tried using my Norton 360 to do file cleanup. Shortly after starting it began deleting literally tens of thousands of Arduino temp files! They had the path users/myname/appdata/local/temp/arduino... followed by varying file names. It must have run for 1/2 hr before other temp files were being deleted. What on earth can this be and how do I prevent them from accumulating in future? I was able to start IDE after the deletion. I have been running brief learning sketches for a couple of months now. Could these be some kind of printed serial monitor output repeating thousands of times if I left my Arduino board connected? I usually unplug it after testing a sketch or put a counter and limit in the active code to a dozen or so iterations so the board can loop forever with little effect. This has only been recently however.