OK. Because of the shell, it can be very difficult to tell if a tortoise or turtle is dead or alive. Dead tortoises usually have the head and all four legs outside the shell. They often appear limp, and feel limp when you touch them. Eyes may be sunken, but that can also be a sign of dehydration in a living tortoise. The eyes in a dead tortoise are usually open. The skin of a dead tortoise may feel warm to the touch, rather than cold. Since the tortoise was cold to begin with, there wouldn't have been a skin change right away if he is dead.
I recommend soaking the tortoise. Make a room temperature shallow bath of 1/2 water and 1/2 unflavored Pedialyte (made for human infants). Soak the tortoise in it for 30 to 60 minutes. Be sure the water is not deep enough to cover the nostrils. Afterward, continue to watch for any signs of movement and keep him warm. You can put him under a basking light at about 85 degrees for awhile.
You could find out for certain if your tortoise is dead by taking him to a reptile vet. A vet could also provide the best treatment if the tortoise is alive, too. This link will take you to a directory of reptile vets:
I wish I could give you a more definite answer, but unless the tortoise is very obviously dead, it's best to give it the benefit of the doubt and see what happens. If you have further questions, just let me know by clicking on REPLY.
(If you find my answer helpful, please click on ACCEPT. Thank you.)