Modifiers

I have been trying to bend a rectagular box and no matter what I do, it won't bend. I've tried using a cube object - increasing the segments and bending, I've made a spline rectangle, extruded it and bending and It just won't go. I've checked the manuals and there isn't a whole lot of information on doing this. Any suggestions? All I want is an arched rectagular box. I've got to be missing something. This shouldn't be that frustrating.