laying eggs

My hens are about 8 months old...why arent they laying yet???:(

Okay, so I have 11 hens that are under two years old and for some reason they have stopped laying. They used to lay 7-8 eggs a day and know I'm down to 0-2 a day. This has been going on for about 4-5 weeks know and I don't know what to do! It has been cold here (I'm in Indiana, and it is...