icons moving?

on my main desktop ill move my icons around the screen and when I turn my laptop off and back on they all seem to have been put in order again on the left hand side
also im sure one disappeared from there the other day
any ideas why? and how to stop it?

thanks

Right click the desktop and make sure you don't have "auto arrange" selected. This may or may not fix your issue. I have manually arranged my icons and they stay in place:

Are you using an external monitor? If so, when Windows boots up, it's probably detecting your monitor change, and rearranging the icons to the smaller laptop monitor.