upgrade to ubuntu 11.10 does not work?

[giovanni de amici]

Good day all;
run into (hopefully) unusual problem, and need help.

Have a Dell Precision 360 running edubuntu 11.04 without problems. Installed via a 'live' disk kindly provided by a friend; played with it for a few weeks to get the feeling of the system.

Computer has 1.5 GB of RAM and whatever BIOS was installed at the factory. No windows OS on it anymore: HD was wiped clean and reformatted a couple of times, just in case.

response to 'uname -a' is:
Linux casa 2.6.38-8-generic #42-Ubuntu SMP Mon Apr 11 03:31:50 UTC 2011 i686 i686 i386 GNU/Linux

wanted to upgrade to Ubuntu 11.10, so downloaded the image 'ubuntu-11.10-desktop-i386.iso' from "http://releases.ubuntu.com/oneiric"

checked the iso file as downloaded with md5sum: passed 
burned the iso file on a CD
rebooted the computer from the CD
rechecked the iso file on the CD: passed
rebooted again, this time choosing to start from the CD and run ubuntu 11.10

the screen appears a dirty white, with an horizontal grey bar at the top, containing a few icons, and a vertical very-light grey on the left side.
not at all like the image at "http://distrowatch.com/table.php?distribution=ubuntu", although it has the same design. just no colors, no structure.

The icons for the applications (firefox, trash, libreoffice, ...) are there; as I roll the mouse over the left edge, small info windows show the name of the applications. But the icons are invisible (transparent?).

when I click on the invisible icons nothing seems to happen: no change in look (except for the title of the clicked icon in the top left corner) and no new window is opened.

The system also becomes non-responsive to the 'shut down' menu command, or to the crtl+alt+del combination, or to any other command I tried. I can only turn off the computer via the hardwired power button.

Rebooted again, after removing the CD, from the edubuntu on the HD; it runs fine.
Checked the memory, just in case: passed.

Since I was booting from the CD, even a defective sector on the HD should have no consequence.

What am I doing wrong? If you reply please consider sending a direct email to my mailbox (sbecd1 at yahoo.it), to make sure I don't miss your contribution.
Thank you for any help.