Before buying a battery you should try rebooting the phone hold down the power button and both the volume up and down buttons, you should get a screen that gives you the option to reset the phone and clear a few things such as the cache and then reinstall stuff. The previous owner probably tried out a task killer that didn't recognize certain things that should be running when the phone starts up and stopped them from starting up or deleted them completely. I had to do this with my phone my phone would power on but shut off with a full battery and wouldn't turn back on without first doing a battery pull and having it plugged in another problem this fixed not being able to receive picture messages too. I'm not pro or nothing just have my one phone and am learning as I go but I hope this helps make sure you have your contacts backed up before the reboot clear and reinstall. Good luck