If you want to start your computer using Windows OS, you should turn it off first, and then press the Power button. To be noticed that the Power button is right next to Latitude ON button which is used to boot into the Dell Latitude ON Reader OS. To change the OS from Dell Latitude ON Reader to Windows, you can also press the Enter OS button which looks like a monitor with a blue curved arrow around it. For more information about this utility, you can read the following article from the official website.