What kind of eggs are they, chicken? Turkey? Are they white or brown eggs? By 7 days, you can see veins in the viable ones. So that is a good sign if you're seeing them, definitely don't toss those. If you dont see veins at all in them, they might be "early quitters". But just to be safe, wait a couple of days and then candle again. If you see a large red ring, with no veining, that means the embryo has died. Toss any you find with that. Make sure to wash your hands before you intend to handle the eggs at all, including candling. Bacteria can get through the shell and kill the embryo, resulting in the "blood ring" that I mentioned.
If ever you are not sure about an egg, wait a couple days- unless the egg is omitting a foul smell (then toss of course).
Good luck, and dont get discouraged if you ask a question and dont get an answer for a while. There are lots of helpful people on this board, but it is a holiday weekend. Someone will almost always get back to you within an hour or so.