Running programs are not displayed in the panel
Maybe the taskbar (Windows List) has been removed?
Right click on bottom panel, that click Add to panel, select Windows List and confirm.
Probably you have removed the Window List on the panel.
Right-click on the bottom panel and choose "Add To Panel" - select the "Window List" applet
More than likely the window switcher got removed from the panel. Simply right click on it, and click add to panel. Then drag and drop the applet on to the panel, and it should be back to normal.