On some rare occasions I find that some parts of the KDE desktop might disappear, like the Start menu or Panel for example. Restarting the KDE desktop is easy in such situations.
Switch to a terminal or open the Run dialog (
Ctrl + F2). Note that this command does not work from a virtual terminal like (
Ctrl + Alt + 1).
If you are using KDE 4.x or Kubuntu 14.04, try:
If you are using KDE 5.x or Kubuntu 16.04, try: