Start Killer removes the Start button from your taskbar. When you run Start Killer it remove the Start button from taskbar and give you additional space on taskbar, when you close Start Killer the Start button is again shows.
Though the Start Button is removed, you can still open Start Menu using CTRL+ESC or WIN key. StartKiller place icon into system tray. Right-click on icon to close StartKiller or to open Settings dialog. You can remove icon from system tray.
In this case use CTRL+ALT+SHIFT+F12 to open settings dialog box