Hi there, let me see if I can help.
1.Since this is a 4 piece kit, test the batteries in some of the other tools to make sure the batteries are good
2. This could be a malfunctioning unit, If you just bought it, take it back to the store and get a replacement, (you may have to take in all 4 and do a complete swap but most home improvement stores have no problem doing this)
3. The Forward and Reverse selector just above the trigger is stuck in the middle meaning, the drill is not in forward or reverse and when you press the trigger nothing happens.
See Page 15 of this PDF for more information.
4. If none of this works, there is a Recall for that Battery Unit.
Check This PDF to see if what you bought applies.Hope this helps.
Brian