MAJOR ISSUE WITH MY CHICKS!!!!!!!!

[poultry for me]

I had a great hatch last weekend, but half of my chicks died!

I think they got too cold.
Here is the issue. They look and act healthy, but then they get weak, sit with closed eyes and appear that they are dying.
Does anyone have ideas to what is going on? I already checked my Chicken Heath Handbook and didn't find any thing. The eggs I incubated were from my 26 week old hens. Would that have anything to do with it??

Any advice would be great.
Thanks

 

[JerseyGiantfolk]

What was the temperature and humidity in the incubator? Or was it in a brooder?

 

[Ilovemyduckies]

What temperature is it in the brooder. For day old chicks it should be kept at 90*, then reduce it by 5 degrees every week.