Help password stuck

If you never set a password for your login, have you tried just entering nothing (leave it blank)?

If you have another admin account, you can log in as that account and reset the password for your other account in the Accounts pane of System Preferences.

If not, you can reset your password by booting from the install disk, going to the Utilities menu then Reset Password and follow the prompts. You won't lose data. You may find that your keychain (which contains your web and wireless passwords) will need to be reset, though.

Matt

Boot from the SL DVD. After the installer loads select your language and click on the Continue button. Wait for the menubar to appear then select Reset Password from the Utilities menu. Follow the instructions.

Note that the above may not work. If there is a corrupted or damaged system file involved you may need to reinstall OS X. Fortunately for you SL can be reinstalled without erasing your files.

So, what you are saying is you get a login screen, enter your password, the login screen disappears momentarily, the reappears asking you to login. You are thus caught in a never ending loop. Am I understanding correctly? If so then try this:

You will need to type some Unix commands. If you are not comfortable with this, I don't know of anything other than a re-install. But if you are careful, you should be OK. I recommend you print this out in a largish mono-spaced font so you don't miss any spaces (or add extra ones). Note that case is important.

Start up in single-user mode. When this has finished you will see a prompt ending in '#', although there may be other messages. Enter the following commands after the prompt:

/sbin/fsck -fy

Press RETURN. Wait a few seconds for 8-10 lines of output. If the last line says repairs were carried out, repeat this command until you get a message 'The volume <yourdiskname> appears to be OK'. Then continue with:

/sbin/mount -uw /
cd /Library/Preferences
rm com.apple.loginwindow.plist
rm com.apple.windowserver.plist
cd /Library/Caches
rm -r *
cd /System/Library/Caches
rm -r *
reboot

Press RETURN after each command.

This should now take you to a proper login screen after the normal boot sequence. You should then Repair Permissions by using Disk Utility (in your /Applications/Utilities folder).