1999 Toyota Avalon Problems starting

When I first get in the car, everything is fine. All the lights come on and the light around the key hole also lights up. When I insert the key it seems fine but as soon as I try to start the engine all the power dies. The lights go off and I can't even use the unlock button in the car. I don't know what the problem is. 2 months ago we took the car in to get serviced and everything was good. The only way I can get the car to start up is if I hit the battery a couple times. The battery is still new though. Could it be the terminals on the battery? When I checked I noticed that one of the terminals is kind of loose.