If no light come on good chance are your battery is dead, you can simply cahnge it yourself.. it's a little 'watch battery'.. CR-something.. Look closely at the key you'll see there a separation mark, open it up and change the battery, you won't break anything
Once the battery is changed it 'should' just work, nothing else to do to bring it back to life, except if it's somehow damaged..
Hope this helps.. Have Fun