Well, assuming it is new, and hasn't been crashed. Also assuming you are using the stock (blue) battery and charger, then I would suggest you check two things:

1. Move your throttle trim up about 1/2 way (centered) or possibly a little higher if necessary before you try to take off.

2. Is your battery fully charged? The manual says it will take the stock charger about 2.5hrs. to charge it, I believe. I found that it actually takes it about 3.5hrs. If you have a Nimh peak charger, use that instead. If you only have the stock charger, then plug it in, and check it about every 15 mins once it has charged for a couple of hours. Don't disconnect it until you feel the battery starting to get a little warm. Don't let it get too hot, however. Once it feel just a bit warm to the touch, it is fully charged 'or close', and ready to use.