The motherboard is threaded but when i screw the screws in they just pop out when i try to lift the board.
Looks like the female (tapped) threads are stripped or the threaded inserts are loose. Use 1/8" longer screws and then attach a nut at the bottom to keep the heatsink assembly secured. Be careful not to short circuit the traces on the underside of the motherboard. This task will need moderate skill.