If you load a model and want to position this model in the assembly it often could be, that the loaded model is not visible, because it is located anywhere outside the viewing area. It would be better., if the loaded model is on the cursor and you can pick the position for the loaded model in the area, where you wanted to position it.
Look to Creo Parametric. If you want to insert a model into an assembly the model is on the cursor. It doesnot matter, what area is visible in the viewport.