Took me awhile to get to figuring out this one out.
You may realise that your numeric keypad doesn’t work after a new install. When you use the 4,6,8 & 2 keys, it may be moving the mouse cursor instead.
To fix that:
System -> Preferences -> Keyboard
That should open a Keyboard Preferences window.
Choose “Mouse Keys” and uncheck Pointer can be controlled using the keypad.
That will give you back you numpad.