Make sure that Windows has not simply "hidden" them to make more room on your taskbar for minimised applications. It hides icons that are not "active" if you enable that feature.
If any are hidden, their will be a small, encircled arrow at the left end of the system-tray. Click on this and the hidden icons will appear.
If you want to see all the icons all the time:
Right-click on the Taskbar and choose Properties.
On the Taskbar tab, UNtick Hide inactive icons.
Click 'OK'