If you have unchecked the option "Display at Start Up" in the AutoCAD welcome dialog and now you want to have it back, use the WELCOMESCREEN command (type it). You can run it as a one-time command or you can check the option again to display it automatically on each launch of your AutoCAD sessions.
The Windows component for synchonization of documents and settings with the Autodesk 360 cloud service runs in the Windows system tray. If there are problems with this component (reports synchronization erros), try to apply the "Autodesk Sync 2013 Service Pack 1" (see Download). If you want - for any reason - to completely disable this resident process (adsync.exe), don't just "kill" it in the Task Manager. Use the Windows tool "System configuration" instead. With appropriate rights, run the Windows utility MSCONFIG, in the "System configuration" dialog go to the "Startup" tab and uncheck the option at the line "Autodesk Windows Components":
AutoCAD commands beginning with "AI_" are interactive LISP commands defined through the file acadNNNNdoc.lsp (e.g. acad2013doc.lsp) loaded with acadNNNN.lsp. This localized file is located in the AutoCAD subfolder - e.g. c:\Program Files\Autodesk\AutoCAD2013\Support\en-US\acad2013doc.lsp. The command AI_DOWNLOAD_LANGUAGE_PACKS opens a web page for download of the respective "language pack" for your version (both industrial and release) of AutoCAD.