Well, where are you now?
Does AutoCAD still load without a menu?
Try going into Options>Files (tab). Expand Menu, Help, and Miscellaneous File Names, then Menu File. What does it say?
This (from AutoCAD Help File) may be of some assistance in the future...(?)
MNU: Template menu file.
MNC: Compiled menu file. This binary file contains the command strings and menu syntax that defines the functionality and appearance of the menu.
MNR: Menu resource file. This binary file contains the bitmaps used by the menu.
MNS: Source menu file (generated by AutoCAD).
MNT: Menu resource file. This file is generated when the MNR file is unavailable, for example, read-only.
MNL: Menu LISP file. This file contains AutoLISP expressions that are used by the menu file and are loaded into memory when a menu file with the same file name is loaded.