AutoCAD 2013/2014 DWG Format

[#1]

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

[#2]

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.

[#3]

You might benefit from asking your MEP peers, as this is for plain AutoCAD which does not have an MEP profile or menus:
http://forums.autodesk.com/t5/AutoCAD-MEP/bd-p/61

Or change to the plain AutoCAD profile, ensure the AutoCAD and not MEP menus are loaded and follow the advice posted around here.

[#4]

Thanks