I don’t know of a keyboard shortcut, but if you need to set the start position for a line, move, or copy, or the the centre of rotation, you can just type [0,0,0] when prompted - that puts the origin as the first point in the Measurement box.
PS. You say in your profile you have ‘lost the box’ for your graphics card.
This should help you find it (the info, not the box) and it helps others to help you if you complete your profile. (Although it starts with info for Mac, info for Windows follows, in the bits you can’t see here).