I installed Ubuntu 11.10 on an old Dell Centrino/512mb machine that was running too slow with Windows to be useful. I am completely new to Linux and muddling my way through as well as I can. The machine still runs pretty slow on Ubuntu. So I loaded the Gnome shell and the classic (no effects) runs fairly well. Everything seemed to be fine up until this. But still not as fast as I'd like.
I read that Lubuntu is even lighter, so I installed Lubuntu-desktop. It still defaulted to the "Ubuntu login" or as I came to discover it's called, lightdm. I changed this to lxdm. Once I did that I suddenly could not login to Ubuntu 2d or Gnome classic (there are a few other options added when I installed Lubuntu-desktop that I also can't login to but i don't even know what these are). When I try to login to Ubuntu 2d or Gnome classic from lxdm it looks like it will load and then returns to the user prompt. I can still login to Lubuntu and others (oddly I can login to Ubuntu, and even more oddly Ubuntu shows up twice on the list). I can also switch back to lightdm and login to everything. I suppose I could just leave it on lightdm, but for lightness' sake as well as consistency, lxdm is nice. And more I just feel like it should work so I'd like to get to the source of the problem.
I looked extensively for answers. The closest I found is an issue for people upgrading from Ubuntu 11.04 to 11.10 and getting returned to the login screen. In that case it was the .Xauthority file being taken over by root (I'm probably saying this wrong). It seemed to be fixed by deleting the .Xauthority file. But since I'm not convinced mine is the same problem I don't want to just start deleting files, the purpose of which I don't even understand. I also found one other post on here with a very similar question, but with no answer.
Any suggestions are appreciated. Thanks.