Oh the poor little guy, cover his cage on three sides this will help him feel safe. Also get some Apple Cider Vinegar but it must have Mother in it. This is a natural probiotic add a couple of drops to his drinking water every couple of days.
Try to keep calm and talk to him, show him the feed dish and water dish, hold some seed in your hand and see if he will take some. Let us hope he is indeed eating properly for you .