[gnome] Xorg hangs on starting gnome-shell or gnome-fallack with desktop effects

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http://ubuntuforums.org – my Xorg hangs when i login to my user in gnome-classic(or shell) with desktop effects. But when i start gnome-classic without desktop effects i can log in fine to the system I am a average user of ubuntu (have tried arch too but it is too much work. though arch documentation is excellent) though gnome-classic (with effects) used to start some while ago... then i was playing around with compiz settings (in no effects gnome-classic) and next time gnome-classic with desktop effects didnt start. I have a sony viao with intel/radeon hd 6630 switchable graphics. I tried installing Arch to it (Hardware)