I assume you know you're charging it long enough, so I won't bother asking that.
Are you sure the charger or charing cord is good? You can get another cord and hook it to a computer, or get one of the USB chargers that plug into a car lighter socket. If that doesn't work, your battery is probably shot. If it does, you solved your problem.
There are Youtube videos about replacing the battery. Batteries for some models can be found on Amazon. I found two quickly. There might be more and/or other sources. There are probably places that will replace it for you for a fee (which might be higher than it should be).