I am completely new to incubating myself, just have my first batch of eggs on day 4 right now, so I won't be able to help I'm sure. If you post what temperature and humidity you keep the eggs at, maybe someone else will be able to help.
That happened to me too. Then I found out I needed to buy a turner. THEN I found out that the turner thingy can fall off the track when you put it in the incubator and it is making noise but not really turning the eggs! All those died. Then I found out I needed to buy a hygrometer/thermometer to keep track of temperatures and humidity. Then I found out that I had my incubator too close to the window. Then I found out that I was keeping the plugs in too long and the eggs were suffocating before they could hatch. Then I found out if I was not mindful of the humidity my chicks would hatch with crippled legs and I would have to kill them as soon as they hatched.
THEN I found out that if I put the incubator up on little blocks to really increase circulation, set it in an open cardboard box lying on it side, with a blanket over it but not completely blocking the open front, set the incubator up on blocks inside the box so there was plenty of air circulating on all sides of the incubator, checked to make sure the turner was working, put the eggs in small side down, laid a sheet of half inch by half inch hardware cloth over the eggs, put my hygrometer/thermometer on top of the hardware cloth, keep a close eye on temps and humidity, running the temp on top of the wire at 101-102 in my still air, humidity at 40-45 percent the first eighteen days, 60 the last three, and kept all the plugs out of the incubator all the time BINGO!!! I had chicks glaore. Then no so much... then I found out that you have to take your incubator apart after every hatch and completely take out the screws, levers, undo the thermostat and completely bleach out and let it air dry for a few days to get rid of the bleach smell, and start fresh again, the hatch rate got good again. Sorry for such a long post, but you have no idea how many trays and trays of eggs I killed before I figured out all the stuff above.
Good luck on your next hatch! Once you get the hang of it you will be up and running and you will be asking us how to stop!
That's why I build my own! If you use a hard plasic cooler IE Igloo, Coleman, Coolmate, you can simply use a disinfectant wipe to clean all hard sufaces and throw the rest into the dishwasher and load it again with more eggs and go take out a loan for all of the feed that you'll need!
You know what! I think that I need to do a tutorial for you guys on building an incubator cheap. It seems that this is a common problem for folks... I really had no idea! I had a hovabator that I got from a friend, after the second hatch failed in the thing, I took it apart for parts. (It's almost impossible to keep styrofoam clean!) Especially when you have an exploding egg in a batch! I got real lucky on my second icubator design... to be continued!