Same here, used to have 24 GB (2x4GB Apple and 2x 8GB Crucial working fine) I got additional 2x8GB crucial and now is not turning on, the only way to had it back was going back to the original 2x4GB Apple(getting worst, and ccs not make it work with 24), looks like some update is blocking the usage of the ram not provided/sold by apple, any clues?