File menu > Reset
Reset clears all data and resets the system settings (viewport configuration, snap settings, Material Editor, background image, and so on). Resetting restores the program to its start-up defaults, stored in the file gmaxstart.gmax, and removes any customization you may have done during the current session.
Resetting the software has the same effect as exiting and restarting the program.
Procedure
If you have made changes since the last Save operation, a dialog prompts you whether you want to save your changes.
To reset the program:
Choose File > Reset.
If you have made any changes since the last Save operation, a dialog prompts you to save them. As further protection against data loss, a confirmation dialog appears.
When asked if you really want to reset, click Yes.
Clicking No on this dialog cancels the Reset operation.