00 Dodge Neon no hot air already changed the Thermostat what do you think you should do next?

i am have the same problem i change the thermostat also and that never worked took it in and they told me the cylinder head gasket need to be replaced so i did that and still didn't work now there saying that the head is cracked so after i get this done i will let you know if that was the problem.to do this it is going to costly i am in to it for about $2500.