Sounds like you got heavier strings on there than what it was originally set up for. It's easy to fix this issue.

1. Turn the guitar over and take off the large cover in the center.
2. Tighten the screws until the bridge pulls down.
3. In the event that there are only 2 springs there, just go to your local music store and buy another one and put it in there. That will also take care of the problem. You will more than likely have to loosen the screws back up a little though :)