When you press down on the SODIMM module after inserting it into the memory slot, note the retention clips on each side of the slot. It’s very important that both of these fall solidly into place. Usually, you will hear a click when the clip snaps into place. If you don’t, the module may not be seated deep enough in the slot. If both clips aren’t properly holding the module, it may jiggle loose and unseat as the notebook gets jostled about.