Thanks to all for suggestions.
Multi Virus Cleaner only turned up a test file AVG uses, no actual viruses.
System Restore was not able to restore to the earlier date, and I am not sure whether Restore in Safe Mode will be any different. It didn't last time I had a problem system restore would not cure. I was advised about redundancy at the time and should have DONE something with the advice.
I have gotten used to right clicking to start music files so I will think about a reinstall when the new hard drive is installed. Just thinking about it gives me the creeps, last time I reinstalled I was most of the way through the marathon when I went out side to look at something green and 3 dimensional to discover there had been a burglary earlier in the day. Not a pleasant discovery at any time and all the more unsettling that I did not discover it for several hours. The consensus was that the miscreant/s had just got inside when I arrived home, only thing missing was a thumb drive I had become quite fond of, and the only comfort was that whoever might well have injured themselves going over the back fence as I entered from the front. Hope the other reinstall went less eventfully.