If your turtle is not moving, then two options are in play. Either your turtle has slipped into a hibernation-like state for reptiles called Brumation or the worse, it passed away. During cold months especially between October and April, turtles are known to undergo Brumation where they exhibit slow to nil movement. They go without food and water for days together and resurface once in a while to hydrate only to go back to brumating.