It could be any number of things. I would first double check the thermometer and the hydromenter in the incubator. How often the eggs are turned also plays a roll.
The following forum may be of help:
http://ponds.proboards.com/index.cgi?board=Call

The link below has a lot of good, basic info. I used to raise hookbills and once pipping started, and I knew the chick was in trouble, I didn't hesitate to help. It's a long tedious process but quite rewarding if you're confident in your ability to help the chick.
Google for more info on aiding a hatchling if you want to try it.

Here is a link that might be useful: Basic info

I dont mind helping at all but they never made it to pipping the one that did make it I helped once I saw it was pipping. Then that is when I checked the rest and they all were dead settled at the bottom of the bigger end of the egg. The eggs still had liqued in it but the duck itself looked dried out at the air pocket end when i broke the egg open to see if they were alive and i did this very slowly and made a small hole with tweezers. I also bought a new thermometer/hydromenter after the first batch did not make it. I also have a auto turner.