No it is not possible to downgrade. You must backup and reinstall. Perhaps
you could tell us some information about your equipment and a bit about your
Linux background. 10.04 was LTS and it actaully has longer support than
10.10. Upgrades always come with risk attached, so it is best to avoid them
whenever possible. You could try to troubleshoot, but we will need some
info. Or you try a fresh installation of either 10.10 or 10.04.

I always install more than one desktop environment and it helps in
troubleshooting. If GNOME does not work then I would try installing the
package kubuntu-desktop. If it works the you could try purging
ubuntu-desktop and re-installing it from KDE. It is easier than
re-installign from scratch and takes only about ten minutes. To use
KDE/Kubuntu you just log out and change the session at the bottom to KDE or
Kubuntu. If KDE seems to drastic for you you could install xubuntu-desktop,
as it is lighter weight.

I think firstly that I mentioned the problem because Greg in
his piece was so adament that it was only Windows systems that froze and
crashed.

As I told him in reply, I have used all the 12 Ubuntu versions and 12 of
the 17 Windows versions, so I am not exactly a beginner in computers
having started on punch cards in the late 70s.

I use this Ubuntu on an older machine with a x86 Fm 5 Model 12
Stepping 9 Intel processor with 2gb RAM. Its on the slave drive dual
booted with XP.

I know quite a bit about Linux have use other Linux systems over the
years but this crashing only happened when I updated to 10.10 so
wondered if anyone had had this happen on theirs.

I will try some options and those you suggest and get back to you.

I have crashed Linux. But is is usually a result of my own foolishness, but
I have also had things lock up and that is usually caused by a poor upgrade.
Things usually straighten up over time. I don't reboot much, but think that
I would see more of it if I rebooted more often. Many upgrades that have
serious consequences only take affect after a reboot or logging out and back
in.

in Windows versions, when you upgrade you are given the opportunity
to save the previous version files so that you can revert.

I have now found that Ubuntu has now followed suit and in 10.10 you can
switch back to 10.4 LTS by logging out.

That would be news if it was true, but it isn't. You cannot revert from one
version to a lower one. Once 10.10 is installed it will replace all of the
root file structure nad it changes the sources list to the new version. If
you have a separate home partition or do an upgrade as opposed to a fresh
installation then it will keep your data and settings. The only way to get
it back to 10.04 (there is no 10.4 BTW) is to do a fresh installation. Many
distributions have been working on a roll back feature, but it is just a
pipe dream thus far. You can roll back parts by apt pinning, but not the
full distribution (at least there is no recommended way).

http://brainstorm.ubuntu.com/item/9625/
https://answers.launchpad.net/ubuntu/+question/18176

You are free to try, but it isn't for the feint of heart and the risk is all
yours. Considering that it takes only 20 minutes to re-install and the
outcome of doing the rollback as shown below could be messy and the results
are iffy at best, it seems to be a major time waster.

https://help.ubuntu.com/community/DowngradeHowto

It did work as I said and that is because I updated. Are you trying to
say it did not work as I said, because It did.

I am saying that you may think that is what happened but it is not likely
the case because Ubuntu does not work that way. You cannot switch versions
at the login screen because the kernel is part of the version (10.04 and
10.10 use different kernels) and those are loaded before the login screen,
from grub. In order to switch you would have to reboot, not just log out and
in. I would be interested in what it says when you type this in a terminal
in each case:

lsb_release -a

All so you can install Lubunu in Synaptic. It is a lighter weight too.

Sounds like a classic graphics crash so have you looked at graphics
drivers ? Also have you done all updates after upgrading ?

Cannot think thats the problem with mine Barry cause the XP side never
crashes and Ubuntu 10.10 installed a great graphics driver that gives me
a wide choice of resolution settings on the desktop.

Did you first download the ISO file of Ubuntu 10.10 and try it as a Live CD
boot? That's how I find out which flavor of Ubuntu and its take-offs work best
for my individual computers. I learned the hard way that updating to a new
Ubuntu doesn't always work.

Thank goodness for Puppy Linux to copy stuff off to USB, since the Ubuntu Live
CD doesn't have a repair option, that I could find.

it was updated from 10.4 to 10.10 by the Update Manager the same
way as I have always done it. And It worked fine and now I can swap
beteen the two versions