Kubuntu is an operating system. Kubuntu is a light-weight variant of Ubuntu.

From '/home/my_user_name/.kde/share/config/kglobalshortcutsrc':


ALT-F2 dolphin: File manager

ALT-F1: Menu

ALT-F2: Run

ALT-F3: Window menu
ALT-F4: Close windows
CTRL-ESC: File manager

Sure, there are multiple reasons. For me it was because of the front speaker (not the master) had its volume set to 0%. Use alsamixer:


alsamixer

(C++) Kubuntu