Chicks dropping dead ..Need help!!

We bought 12 that are 6wks old from someone who got the rare breed pkg. from McMurray. They started out fine but now they just stand with their eyes closed and cheep loudly. They seem to eat and drink but not as normal chicks do. The only sign of any kind ..I heard one cough or sneeze this morning but thats it. They are dropping dead 1 a day. Any ideas whats wrong?

Thanks in advance
John

Have you gave them Sulmet in thier water. I always start them off with sulmet in their water. did not have any problems with my chickens this year from that but the guinease did even though I gave them this. And sometimes it is ithe hatchery. That was what was wrong with the 30 guineas I got I have 1 left. They would drop dead one to two a day until I had none left. They did not and sill dont want to deal with it. I did not get them from mcmuarry.