unable to log-in to ubuntu 12.04

What happens when you try and log in as your user?
Why do you not have a backup?

@actionparsnip (andrew-woodhead666 ) when i enter my password a black screen appear and after that log-in screen again apear.just like a cycle.
no i do not have a backup.

I didn't ask do you have a backup, I'm asking why you don't have one? Is your data not important?

my data is important to me but as i am new to ubuntu i dn't know that installing a software(i.e oracle) will cause this much damage.

You should still have a regular backup, Oracle software or not..... It's nothing about being new to an OS. If you can copy and paste files to a folder, you can backup. No excuses.

If you press CTRL+ALT+F1 and log in there, run:

df -h; lsb_release -a

What is output please?

my bad about backup.
after CTRL+ALT+F1 i am still getting the same thing ,some message and after that again login line.
unable to read message either welcome/eroor message .

Hi ,

bellow steps hopefully will solve your problem , but follow them with caution.

1. Boot from [Recovery Mode] . Usually is the second selection in grub menu (if you don't have grub menu hold down SHIFT key during boot until menu shows up)

2. From the window that appears select ROOT and press ENTER key.

3. Now pay attention and give bellow commands with order and replace the username with yours.

a.) mount -o rw,remount /

b.) chown username:username /home/username/.Xauthority

AGAIN : Replace username with your own and attention when give the command. Before X(authority) is a dot and X is capital. Everything matters when you write a command . Capitals ,spaces, dots , colons, backslashes, commas... everything.

4. Finally reboot your PC with this command
reboot

Thanks

this is not woking.
finally i decrypt my home folder and copied my data.
thanks all for helping me.

Encryptfs is a massive pain, I personally avoid it due to the amount of headaches it causes.