Windows XP and above automatically hides inactive tray / notification icons. Generally speaking this behaviour is not ideal and can be disabled using the following instructions. Right click on the Start button and select Properties. Click the Taskbar page and uncheck the Hide Inactive Icons option. Once OK is selected all hidden icons will be displayed. If you wish to have more flexibility (or if you are using a newer operating system and the Hide Inactive Icon option is not available) choose the Customize button on the Taskbar page and then select which icons you wish to show or hide.