Hi, this could have multiple reasons. The most common ones to check are:
1) is the models visibilty set to 1
2) is the displaylayer (layerlist is bottom right under the channelbox ) tha contains the model set to visible
3) In the viewports "Show" menu, are polygons checked true for display
If it isn' any of these, please upload some more screenshots, especially one with the model selected in the outliner and hierachy above it expanded
I hope it helps!