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.