I installed Ubuntu 12.04.2 LTS yesterday and tried to change from unity2D to the default unity3D environment but my laptop got stuck only showing the default wallpaper and the mouse pointer.
After 5 minutes I decided to turn off my laptop manually (with the power button).
Now when I turn on the laptop and choose Ubuntu from grub it only displays a black screen.
I can now use Ubuntu only in recovery mode and I want to change session from Ubuntu to Ubuntu 3d to see if it will help.
My laptop is a HP ProBook with switchable graphics (Intel hd and radeon hd 6490m).
I had a lot of trouble installing the Catalyst drivers, and now I can use Catalyst Control Center but in 'system info' in the graphics driver section the driver is still displayed as 'unknown'.