Make sure the puppy is not chilled as a chilled pup can't eat and digest food. If the pup feels cool warm him up.
If you know he's warm enough then try a drop of Karo or pancake syrup on his tounge to give him some energy to help him get strong enough to nurse.
You can also milk the mother dog's mammary glands into a small glass and put drops of mom's milk in his mouth one by one (make sure it stays warm - keeping it near a light bulb can warm it enough).
If you are hearing lung congestion in his breathing he may not have all the fluids out of his lung area. Sometimes holding the pup at a downward angle, belly down and head down, will help drain fluids from the lungs.
You can read about fading puppies here
http://www.showdogsupersite.com/kenlclub/breedvet/fading.html
Sadly not all pups are able to live to grow up. Some have birth defects that keep them from thriving.
Check in the pup's mouth to see if he has a cleft palate or opening in the hard palate that is keeping him from being able to nurse as he can't get any suction going. If you put milk in his mouth and it comes out is nose that can be a sign of this birth defect.
Hope this helps you!