The strange thing happened after I did move my specific *.directory and *.desktop files to symbolic links. I haven't got a continuously rebooting n900, but it was never showing the menu again... GUI hangs if I did click any shortcuts or menu button instead. The good thing is that Ctrl+Shift+x works for me to start the terminal and sshd. It may be a reason for such a behaviour that I did execute cache update for icons along with menu/symlink modification. The other strange thing is that now it is working with all changes I did right before I had get the "menu hang"...