the problem is due to the hinge inserts being set in weak plastic.. over time they become fatigued.. there's loads of sketchy ways people have suggested fixing this on the internet - the only real way to fix it properly - is to order a new replacement palmrest (it will have the plastic supports and threaded inserts for the hinge) - then just transfer over the motherboard etc into the new palmrest.. before re-fixing the hinges - unwind them half a turn.. also fill in the gaps between the plastic mounts with epoxy to add a bit more reinforcement and you shouldn't have any problems in future.