For this you will need to use the Move command. Select all the components in your model and start the move tool. Click the Up To option (shortcut key: U) and click the world origin. This should get the center of volume onto the world origin. To orient further, you can place the Move tool on an edge that you know should be aligned with one of the X, Y, or Z axes. Click a single axis handle on the move tool, then click the Orient to Object option from the Move tool options. Click the desired axis on the world origin and the model will align to that.