I was a huge fan of Gnome-shell, much better than Unity-shell, but I'm unable to run it since a few weeks. When I try to log in with Gnome-shell session, I'm able to see only the background image. None of startup apps appear, nor top panel.

If I start Unity session and type in Ctrl+Alt+F1 terminal:

user@home-PC:~$ gnome-shell --replace
Window manager error: Unable to open X display

or in gnome-terminal after:

user@home-PC:~$ gnome-shell --replace
Segmentation fault (core dumped)

it freezes until I type unity/gnome-panel –replace in Ctrl+Alt+F1 terminal.

EDIT vol. 2.0:

THERE IS THE SOLUTION:

I found what was the problem. Actually very simple, but never met this before. The PPA had two versions, first one, the normal 3.4, but the second one was 3.5 or even higher, which does not work on Ubuntu 12.04. I've checked mine with:

gnome-shell --version

So the only thing I had to do is to select the correct version to install, then everything works fine. Thanks for the help. 🙂

EDIT:

I reset my Gnome-shell settings following steps from here:

rm -rf .gnome .gnome2 .gconf .gconfd .metacity .cache .dbus .dmrc .mission-control .thumbnails ~/.config/dconf/user ~.compiz*

and right after it:

gnome-shell --display=:0 --replace

and it worked fine, even after rebooting.

After that I added some ppa-s and installed some gnome-shell-extensions and gnome-tweak-tool and rebooted. After trying to login, Gnome-shell crashed again, this time in terminal:

user@home-PC:~$ gnome-shell --replace
(gnome-shell:4067): GLib-GIO-ERROR **: Settings schema 'org.gnome.desktop.a11y.magnifier' does not contain a key named 'invert-lightness'
Trace/breakpoint trap (core dumped)

So I need help again. 🙁

BEFORE EDIT:

I've tried several things:

Renaming ".gconf" in user "Home".
DISPLAY=:0 gnome-shell –replace

STATUS: still not working Gnome3.

purge fglrx:

sudo sh /usr/share/ati/fglrx-uninstall.sh
sudo apt-get remove --purge fglrx fglrx_* fglrx-amdcccle* fglrx-dev* xorg-driver-fglrx
sudo apt-get remove --purge xserver-xorg-video-ati xserver-xorg-video-radeon
sudo apt-get install xserver-xorg-video-ati
sudo apt-get install --reinstall libgl1-mesa-glx libgl1-mesa-dri xserver-xorg-core
sudo mv /etc/X11/xorg.conf /etc/X11/xorg.conf.backup

and reinstall it via Graphic interface or using this.

STATUS: still not working Gnome3.

purge gnome-shell:

sudo apt-get purge alacarte cups-pk-helper gir1.2-accountsservice-1.0 gir1.2-caribou-1.0 gir1.2-clutter-1.0 gir1.2-cogl-1.0 gir1.2-coglpango-1.0 gir1.2-folks-0.6 gir1.2-gconf-2.0 gir1.2-gdesktopenums-3.0 gir1.2-gee-1.0 gir1.2-gjsdbus-1.0 gir1.2-gkbd-3.0 gir1.2-json-1.0 gir1.2-mutter-3.0 gir1.2-networkmanager-1.0 gir1.2-panelapplet-4.0 gir1.2-polkit-1.0 gir1.2-telepathyglib-0.12 gir1.2-telepathylogger-0.2 gir1.2-upowerglib-1.0 gir1.2-xkl-1.0 gjs gnome-applets gnome-applets-data gnome-contacts gnome-icon-theme-full gnome-panel gnome-panel-data gnome-session-fallback gnome-shell gnome-shell-common gnome-themes-standard indicator-applet-complete libcaribou-common libcaribou0 libclutter-1.0-0 libclutter-1.0-common libcogl-common libcogl-pango0 libcogl9 libgjs0c libmozjs185-1.0 libmutter0 libpanel-applet-4-0 mutter-common python-gmenu

and reinstall gnome-shell:

sudo apt-get install gnome-shell

STATUS: still not working Gnome3.

One of my biggest mistakes:
purge and reinstall all gnome* packages – doesn't work, even I lost some apps, now Unity and Gnome-panel work fine, except Gnome3

STATUS: still not working Gnome3.

reinstalling all available Ubuntu packages:

sudo dpkg-reconfigure -phigh -a

returns:

** (accounts-daemon:7108): WARNING **: Failed to acquire org.freedesktop.Accounts
** (accounts-daemon:7108): WARNING **: Could not acquire name

and after 30-40 minutes the finished.

STATUS: still not working Gnome3.

So I hope anybody help me, I love Gnome-shell, but I'm disabled to use it. Thanks in advance. 🙂