I Tried to change the settings using unity in compiz cube. I went to opacity settings in Unity tool and then clicked on new and then on '+' sign and then clicked on grab, then I clicked on the same window and by mistake set its opacity to 0 now I am unable to see the window and change the settings please tell me any solution for this problem.
You can start Ubuntu in Recovery Mode(Usually the second option in GRUB).
Recovery Mode disables most advanced graphics settings, So everything will look normal and ugly (and safe!) like before.
You can then start CCSM and reset that faulty setting.
One advantage of this over the
As a precautionary hint, take the dialog which pops up when you start CCSM pretty seriously! CCSM IS quite a dangerous tool.