I tried to cook croissants following a recipe. The whole process went smoothly, there was no butter melted and the yeast was still active. But when I proof the laminated dough, they wouldn't rise. I prove them in the fridge overnight because of the hot weather (The average room temperature reached 30°C.), but I found that the butter became solid and I think that's why the dough didn't rise. I've made some research and I found that a lot of people proof their laminated in the fridge successfully. What should I do now?
30C is a good temp for proofing. Proofing overnight in fridge allows for greater flavour development in breads (or any yeasted dough), but they still need to be proofed further at room temp before bake. Croissants I have never seen proofed in the fridge - not saying it can't be done, but I've never seen it. The only time you should be truly concerned about a hot kitchen (in my opinion) is when you're working with chocolate. Because breads and yeasted things rise best between 27C and 38C with the optimum temperature being 35C. Check out this link for more info http://www.theartisan.net/dough_fermentation_and_temperature.htm
Good Luck! Croissants are a labour, but a delicious one!