I am using AutoCAD MEP 2013
I cannot find the ribbon for 3d Modeling the one that contains EXTRUDE commands and others
There is no selection in the upper left corner that switches from standard to 3D Modeling or anything else
Have you changed workspaces? Does your profile support it? The AutoCAD base profile has 2 workspaces that support 3D modelling. Select the profile, then the workspace.