As the Life Orb inflicts indirect damage, Magic Guard prevents a Pokémon from taking damage from the Life Orb. If a Pokémon with Sheer Force uses a move boosted by that Ability, it does not take damage from Life Orb for that move.
Sheer Force and Magic Guard are the only Abilities to negate Life Orb damage. Klutz does as well, but a Pokemon with that Ability won't receive the Life Orb boost anyway.
Life Orb (Bulbapedia)
