Ever had AutoCAD Architecture/MEP just "disappear" when opening project? It’s not a fatal error, not a crash, but the main window and task bar button is gone. Floating toolbars, Palettes and other UI items may still be displayed and work normally (even the command line). The reason is a valid acad.exe process is still visible in Task Manager. It’s gone, but it’s there, but it’s gone!
From my investigation this happens in ACA/AMEP 2008/2009 (see this Discussion Group thread) and the cause seems to be corrupt Project Profile settings. If you shutdown the application and delete the problem config file normal behaviour is restored.
You can shut down with the command line, using "exit", if it’s still visible and you'll be prompted to save any unsaved work. If the command line not visible select something which is, to give the invisible application focus, then try Control+Q to exit AutoCAD. If none of that works right click and end acad.exe in Task Manager (CTRL+Shift+Esc).
Delete your personal ProjectProfiles .aws file. These are re-built after deletion but you will loose project specific customisation. Open this folder:
C:\Documents and Settings\[LOGON]\Application Data\Autodesk\[APPLICATION_NAME]\enu\Support\Profiles\ProjectProfiles
You can delete all or just delete the problem project.aws. To find that open them with Notepad. The "Name=" section shows which project has generated the .aws. Once that’s done launch ACA/AMEP with a full user interface again!