Even if the charger shows the battery fully charged, leave it plugged in on the charger for a few additional hours. Maybe even overnight if the battery and charger don't feel "uncomfortably" warm. Place it back in the camera and wait a couple hours before attempting to turn it on.
Try removing the memory card if one is installed. With the card out use a lighted magnifying glass to inspect the card slot to see if any of the contact pins are bent or damaged, or if there's any signs of corrosion. If so then it's probably "game over". It's not an uncommon problem if somebody has been careless and forcibly inserted the card when in a hurry.
Do you know anyone else that might have a similar battery in known good condition that you can try? Maybe a local camera shop or camera club member could help you out.
Both the battery and memory card doors are fitted with micro-switches so that the camera can't power up if either of them are open. You may find that the camera will respond differently if a little extra pressure is placed on or around the closed doors.
Does the camera appear to be in good cosmetic condition? Or does it show signs of heavy usage or abuse? Good luck trying to bring it back to life. If you can get it fired up it should make a perfectly good beginner DSLR.
