Comment 11 for bug 1756585

If I create a new user, "unity" starts fine (for this user).

This implies that the problem depends on the configuration of an old user (created under Ubuntu 12.04).
"https://askubuntu.com/questions/17381/unity-doesnt-load-no-launcher-no-dash-appears/" suggested to fix the problem by "dconf reset -f /org/compiz". This did not change anything for me. Neither allowed removing "~/.config/dconf/user" a successful unity start.

I will now try to find important differences in the configuration for the old and the new user.