I noticed your post is 5 days old and you may have figured it out. If so, please post that you figured it out and how you fixed it to aid others with same issue.
If you haven't got it up and running, please leave a little more information on what lead up to it happening. If you dropped it, had water damage, are you using the original charger or a generic charger, etc...
You may want to make sure your charger is good and charging your phone ok...also check the charging port for any debris or damage to make sure it is making contact. If you are experienced with a multi meter, you can open the phone, disconnect the battery and test the battery directly to see if it has a charge and post back the results. Then you can test the voltage at the battery connector with it plugged in to make sure your battery is receiving a charge from the charging circuit.
After trying the above suggestions, post back the results and we can go from there :)