First thing to do is to check the circuitbreakers in the panel. If it is an older house that has fuses, it gets a little harder as it's not always easy to tell if the fuse is blown. On a CB panel, if the handle is not fully to the on position, you'll have to push it fully to the off position, then push it to the on position. Turning a CB on or off takes a lot more pressure than a light switch, so don't worry about that. If it won't stay in the ON position, there's a short of some other problem in the cuicuit and you probably need to call an electrician.