CryEngine manages its ram usage on its own, it should exceed 750 after loading the simplest of maps. First off make sure there isn't any kind of PC Performance app trying to mess with it. Second, if there is nothing screwing with, trying restarting the computer a few times. Third, if that doesn't work try redownloading CryEngine.
BEWARE: Flaming aliens are generally more grumpy than normal ones.