if i go to add > mesh > cube, a cube appears onscreen. The expected result also happens for sphere, cylinder, plane, and even the monkey head. Probably all the others too.
But when i use add > mesh > torus, nothing appears. A torus object is created in the heirarchy, but it seems to have no geometry. i cannot enter edit mode with it selected, whatever it is. i can’t see anything or do much with it. it’s a torus that doesn’t exist.
Nothing that people are likely to figure out with the provided information.
Check that you’re using 2.72b from the splash screen. File -> load factory settings. If it happens in a saved file, the scene might be broken for some reason. In that case could try appending all objects to a new one with file -> append.