The next key down from the g key towards the foot may well not be closing. Turn the flute so the pads face you, and the key next to the g key is to the g keys left. now push down the g key, if the other key isn't going down all the way, look for a screw on top between the 2 keys. get a tiny screwdriver (flat head), insert into the screw and turn while holding the g key down. if the other key raisies, screw the other way. turn until both keys go down at the same time.
you will no doubt find other keys are in the same condition of not going down. you need to locate each ones screw, and align the keys.
normally this would be done by a professional at the yearly service, which sounds like it needs. However, if it is a cheap chinese flute, you will most likely be doing this on a weekly basis.
Good luck, and if all else fails, find a teacher to show you how to do it.