How long have you had it?
If you just brought it home then chances are it's still acclimating to the tank. They can take a few days to adjust and start eating.
Did you see it eat at the lfs
If you bought it at a lfs
, call them and ask what they feed and try some of the same. After 3 or days it should be hungry enough to eat almost anything. You can try some Garlic Xtreme or pure garlic juice on the food. JUST A DROP OR TWO! It's very powerful and considered a great food attractant as well as prophylactic for Ich and other parasites.