In AutoCAD 2009, Autodesk introduced the ribbon interface to AutoCAD. The ribbon is their new alternative to toolbars and pulldown menus.
To get your pulldown menus back, type MENUBAR, then 1 at the command line.
In AutoCAD 2010 and higher, our software displays a ribbon instead of toolbars by default. If you prefer toolbars, the easiest way to get them back is to use the “DM H/E/P->Utilities->Find Lost Toolbars” command (replacing H/E/P with “HVAC”, “Electrical”, or “Plumbing” as appropriate). This will display all of our toolbars. Dock or move the ones you want to keep and close the ones that you do not.