I had been working at my desktop yesterday and left it for a break. I returned to find the Welcome screen. I logged in and discovered everything I had been working on had closed. It was extremely fortunate, and a reminder, that I had saved a long text file I was compiling. Reliability Monitor showed the culprit to be App Readiness as an application failure. We can be sure something new will always appear. I have no idea about App Readiness and what is likely to have caused its sudden appearance.