I am upgrading an Ubuntu system from 8.04 to 10.04. In view of various warnings, I decided not to use the update manager, but to use the 10.04 Desktop install CD.

I had a dual boot Hardy with windows.

Now I have a strange pseudo Lucid windows!

On startup it gives the usual Grub selections. All good so far.
On Selecting windows, it runs fine. Again no problem.

On selecting Ubuntu a standard login screen is displayed with the usual dialog box.

After typing the password, the system pauses and then loops back to the login screen.

If I abandon the graphic and go for a command line login, that seems to work ok. But there is no sign of graphics and a desktop.

I know that this is not very complete info, but, since the system worked fine before the upgrade, it is hard to know where to dig.

Any ideas?

After getting the log-in error. <CTL>+<ALT>+<F2> to get a terminal, log-in and look at .xsession-errors file. This should tell you where the problem lies.