Why Isn't My Phone Coming On?

I've had my Centura for almost three years and i've only had minor difficulties. Not to long ago, it would be fully charged but shut off within fifteen minutes or less. I assumed it was just the battery so I bought a new one online. The new battery made the phone work perfectly for a few days. But one day as I was about to go charge it, (it was on 15%) the phone went off. I charged it over night but when I woke up and tried to turn it on, it would only show "Samsung" across the screen for a moment then turn off. I have important things on the phone and really need it to come back on. Is there anyway it can be fixed? Thanks in advance.