I'm glad to hear that he opened his eyes and ate a bit yesterday! I suggest measuring the temperature (I've used a thermometer before) where his shell is under the heat source to see if it is the proper temperature. It seems like he may want to be warmer since he is sitting under the heat source...
I also agree with the suggestion of soaking him for 30 minutes in a little bit less than chin-deep warm water. I would suggest repeating the 30-minute soaks every 1-2 days for a while until he gets better. But I agree with determining more information with the questions about diet, heat, etc. above.