Troubleshooting menu issues
If all your application menu icons and programs disappeared after installing a new app, check that the space on your root filesystem has not been (almost) completely filled. You can see the remaining space by opening an xterm window and issuing the command
df -h
Check the output line where the column "Mounted on" corresponds to "/". If that partition has been used by 99% or 100%, chances are your menu has disappeared for this reason.
The next thing is to free some space. Most likely, you will be able to get rid of some multimedia files in /home/user/MyDocs/.images or /home/user/MyDocs/.sounds - but check also .documents and .videos.
After this step, the right command to see your menu again will be
cp /etc/xdg/menus/applications.menu /home/user/.osso/menus/ ; update-desktop-database
NOTE: this must be issued as root. You have a root enabling package installed, haven't you? See Root access for details.
Thanks for this tip to Faheem (qwerty12 on internettablettalk.com forums).