My desk top today (02 May 2016) has been altered and all my icons have been re-arranged how can I alter them back as they were yesterday (01 May 2016).
My old computer, running Vista, sometimes does this. I just power it off by pressing the power button BEFORE I do anything on it (not recommended normally) and restart it; it then comes up normally.
If you've done things you can re-arrange the desktop by dragging the icons to where you want them. Hopefully it will start up next time with the icons in that position.