Hello people! I've been using linux for a while and this problem never occurred until today. And I've searched some solutions online and tried them out, no use at all.

The problem is:
I can't login on desktop even though I entered the right pssword. After I entered the right password, it seemed to be logging, but then it switched back to the log-in page. Like this, over and over again, just won't let it in.

My system is:
Ubuntu 9.10 karmic

It still worked normally yesterday, but this afternoon it's like this. I have no idea why. Does anyone know what's wrong? How should I solve it?

According to what I found online, I've tried to remove gdm and re-installed it; failsafeGnome; autoremove to free some space. No use, still the same.

I'd appreciate any help/ideas. Thank you in advance!

When I had this problem before, it was because the disk was full and couldn't write the necessary files for starting the desktop session.

You say you've cleared space though and are still having the problem. I wonder if you have ssh-server enabled you could try logging in over ssh - It could help narrow down the problem.

first of all, have you tried to look at the system log on stdout? its normally on f12 as in ctrl-alt-f12. it mostly a copy of /var/log/messages

secondly, have you installed anything new recently? like oracle for example?

thirdly, and this could be related to the second. have you edited any files in /etc/pam.d ?

and finally, have you tried logging in with rescue mode?
- use rescue mode
- mount your hard disk
- chroot the new mounted directory
- su - $user
- read the error message

Thank you for your replies!

@zugvogel
Well, I have tried to free some space by autoremove, which freed 300 MB. And I gave Ubuntu 50 GB (I have duel systems), so it should be enough, I guess?

@marafa
I don't think I've edited pam.d nor installed something like oracle (no idea what it exactly is). Just to be sure, in which situation could I actually edit pam.d without any notice? I just recently edited the layout of the desktop, I guess that's it. I have used rescue mode (if it is also called failsafe?) to change the password to try logging in, no use. I could only log in under safe mode, and after finally re-enterring my desktop, there were no menu bars at all, and if I opened a file or a folder on the desktop, the windows did not contain those close buttons and such. I'm sorry that I'm a beginner, so could you explain how I could do the mount and chroot things safely? :| Thanks a lot.

Oh sorry that I messed it up with failsafe stuff. I did have used rescue mode...

I appreciate any further help

Ah, thanks everyone. I've fixed it myself by solving every problem (more than not being able to logging in) under rescue mode...