HP ProDesk 400 G4 Maintenance And Service Manual page 83

Mouse will only move vertically, horizontally, or movement is jerky.
Cause
Mouse roller ball or the rotating encoder shafts that make contact
with the ball are dirty.
Solution
Remove roller ball cover from the bottom of the mouse and clean
the internal components with a mouse cleaning kit available from
most computer stores.
Solving keyboard and mouse problems 75