Ok, if I am understanding what you are saying you have a tablet that you have had off for a year and now won't work? Well in that case the battery is probably needing replacement.
If you mean you have had it for a year, and now all of a sudden it isn't turning on, then I would check to make sure the charger is actually working. I suggest trying it on another device. If the charger works fine, then again, you probably need a new battery.
If your tablet is still under warranty, then I would contact the manufacturer about having it repaired or replaced. If it isn't under warranty anymore, then you are free to try replacing the part yourself (there are tons of videos online on how to do so) or take it to a local repair place to have them...