Get a big bowl of warm water and float test your eggs. This will tell you if they're still alive in there and have any chance of hatching. Water should be 99F - just the same as the temp inside the bator. Let the bowl sit for a minute till the water stops swirling around. Then put the egg in it, wait a minute for it to steady itself, then watch for rocking and ripples. If it sinks, that's bad. If it floats really high in the water, that's bad. If there's a live chickie in there it will make irregular wobbling movements and there'll be ripples in the water. If it goes still and doesn't move in two minutes then that's most likely bad too.
If you've got a live chick just dry the egg off carefully and return it to the bator. And wait...
I only read about this method about two weeks ago and I've used it three times since then, with very accurate results. Two dead in shell and one live chick that went on to pip and hatch normally, all by itself with no assistance. From now on I'm going to use it on every egg that hasn't pipped by the end of day 21. It saves a lot of time and hanging about trying to convince yourself they could still hatch on day 25, 26, 27 even, cause someone else on BYC had that happen to them...