How do you know your eggs were fertile? Even if you have a rooster with hens it doesn't mean that the eggs are fertile. Some roosters aren't fertile. Even a highly fertile rooster wont take care of all the hens. They will have their favorites. So not all the eggs would be.
There is a chance that you could check one egg and it is the only fertile egg you have as well.
if on day 7 there is nothing in the eggs then they simply weren't fertile. something would have developed. If it were an incubator issue they would have started to develop and then stopped/died.