When you candle it can you see a shadow in the air cell at all? If the embryo has died it will look very black and sink towards the narrow end of the egg. There will be a watery gap between it and the air cell. If the egg still looks full I'd just wait a little longer - it may have been sitting in a cooler spot in the incubator. If you can see a shadow in the air cell that's the chick's beak having internally pipped. If you put the fat end to your ear you can often hear tapping (but listen for awhile as your fingers or hair rubbing against the egg will make a noise too - you are listening for a rhythmic tapping). I find those methods easier than trying to float the eggs. The air cell looks like it has drawn down which is a good sign.