Ubuntu Login problem using GUI interface

I have been coming around with this problem from long time and there is no fixed or predefined solution for this. May be its there but its not in my knowledge. Every time I found different reason of this problem and fixed it. So thought to write some of those issue here and there solution.
Since you are not able to login through GUI but you can still login using terminal. Press & [F1-F6] to get terminal and press to get GUI window.
Now here is different issues:

1. Permission of file "/home/user/.ICEAuthority & /home/user/.Xauthority" might have changed. You check file permission using "ls -la ". If write permission is not given to user then change permission to particular user.
Other thing you can do is "sudo chown user.user /home/ -R"

2. Check if "/tmp" directory permission has changed to root only. If read only then changed it to 777.

3. you can try to run this command "sudo /etc/init.d/gdm restart" on terminal. After that run "sudo gdm" and you will get GUI interface to login. Provide user information and login and if you get success then restart the system. Now you can do normal login. some time it works fine for me!!

some other problems are also there but i m not sure whether they are related to above said problem or not. So I am skipping those issue, may be I'll write later :)

PS: all above solution are hit & trial solution based on what problem I have faced.