My turtle is not eating and is not swiming around like the day it came?

i got a red slider as a gift and the day it came we kept it in a tank with 2 inches of water like the person asked us to and we gave him turtle food and pebbles and a place to sit out of water just a little above the water and he is kept in a well lit area we change the water regularly but no filter and no uv lamp ........is that the cause???i really want to help it Please suggest something!!