You could troubleshoot this, go back to the defaults, or change to a desktop that does what you want: see links below.

Which version of Ubuntu? The current version (11.10 Oneiric) uses Compiz by default so you would not have to install it.

Was what you installed the Compiz Config Settings Manager (CCSM)? You would need it to enable the cube.

For an immediate login you can probably still login to unity 2d (on Oneiric) or Ubuntu Classic (11.4 Natty). Options are next where you type your password in (Oneiric) or at the bottom of the screen (Natty), assuming you have not changed the login theme.

Once logged in you could try running CCSM and checking that the Unity Desktop plugin is enabled.

For either Oneiric or Natty you could try the solution here:

[ubuntuforums.org ]

If its a pre Natty version, you should still be able to login without Compiz, but I cannot remember what you should choose.

If you are using the Unity desktop (default on 11.04 and later) or later it is best not to mess about with Compiz settings unless you are willing to risk having to solve problems as the Unity desktop relies on some Compiz settings. see [tuxgarage.com ] which also links to a page with some possible solutions. If using Unity, CCSM is a geek tool for those willing to mess around (which is why you need to install it separately)

If you want the desktop cube, or to customise your desktop in other ways, you probably should not be using Unity which is the least customisable Linux desktop I have tried - it works very well as it is (I like it), but your choices are restricted.

For that case would suggest Kubuntu. You can add Kubuntu to your existing Ubuntu install by installing kubuntu-desktop, either from the installer (Synaptic or Software Centre), or by switching to a terminal (which you can do with Ctl-Atl-F1 ) and typing:

apt-get install kubuntu-desktop

then reboot

Incidently, Ctl-Alt-F7 should get you back to the GUI screen from the terminal.

Unless your hardware is old or low powered Compiz should work . It works (OK rather than well) on my netbook.

Thanks for the detailed reply. It was the latest version 11 point something, so it must have been the Compiz Settings Manager I installed. I decided to reinstall Ubuntu (first time I have ever had to reinstall an OS, never even for Windows!).

The problem was, I had selected automatic log in and couldn't select a different user interface during log in. The only way I could see was to use the system was in "recovery" mode. Disabling the desktop cube in here and restarting didn't work. I hadn't seen that there was a "Unity Desktop" plug-in that probably needed checking again.

I have installed KUbuntu and this tells me that the hardware isn't quick enough for desktop effects and it disabled them for me - it an old laptop (1.6GHz, single core) that I am testing with.

Yes probably best to avoid desktop effects on old hardware.

You could have logged out - Ct;l-Alt-Delete would have done it.

I like Ubuntu Unity, but if you want customisation you are better off with KDE. Now you have it working, you might also try XFCE and LXDE: faster on older hardware and almost as customisable as KDE. On Ubuntu, LXDE is probably best as Xubuntu is a bit bloated for XFCE.

Glad you got it working. Linux is very stable per se - but it does allow you to muck it up yourself, which is very tempting for those like us who cannot resist the urge to tinker (I have a good many problem with Linux, my wife, my kids and my father all have very few problems).