I assume a tama would be like most other electricals, you should keep them in a warm place, but not so hot it bakes... once your tama warms up it should come back to life If water got in it however it might be a different story..
this has never happened to me so i might not give the most accurate info, but i think theres a liquid in the screen that freezes. *rumor* so once you put it in a warm place it will be fine.