I have faced a similar situation while installing Arch Linux and Cinnamon.
In my case, if I logged in using Cinnamon, the Gnome desktop was shown. Nevertheless, if Cinnamon (Software Rendering) was used, everything worked as expected.
Cinnamon is the 3D accelerated version, thus, depends on the installed graphic card. Since it was not working, I had a problem with my graphics cards drivers.
My laptop, a Dell Inspiron 5547, has an Intel Integrated Graphics Processor (IDP) and also a Radeon R7 M265 Dedicated Graphics Processor (DGP). Once I installed the correct drivers and enabled hardware video acceleration everything worked like a charm.
Driver for Intel Integrated Graphics Controller
# pacman -S xf86-video-intel mesa lib32-mesa
Driver for Radeon R7 M265
# pacman -S xf86-video-ati mesa mesa-vdpau lib32-mesa lib32-mesa-vdpau
Enable hardware video acceleration through VA-API
# pacman -S libva-intel-driver libva-vdpau-driver