That hard to address without seeing the actual instrument. Look to see if any of the keys aren't closing all the way. To do this, just finger the low c and just look to see if any of them aren't closed all the way. Since you said g is not working the key that's not sealing is most likely the round key on the far side of the left hand pinky key. It's one of the ones that doesn't have a finger on it. Still that is only my best guess without seeing the instrument, and with the information you gave me.
Though, that mostly just allows you to pin point the problem. Unless you know which screws effect which keys, I would say just take your flute into your local instrument repair shop.
If you wish to take the risk of trying to fix it yourself and would like help or guidance you may ask me at Charmed1P5@yahoo.com. Though keep in mind I'm no professional flute technician, I've learned from trail and error on my own flute and by watching over the shoulder of the trained person that fixes my flute.
Harumi
October 2007