After executing Reboot command from root user,my normal user account is not opening up even with correct password,instead it is rebooting again!

view story

http://askubuntu.com – I typed su to get superuser privileges in my ubuntu 12.10 and then typed startx to start the x-server.After the x-server started successfully,i typed reboot command.It gave a broadcast message printed on the terminal and restarted.Login screen appeared.but even when i typed correct pasword,the useraccount is not getting unlocked.instead it is rebooting once again.i have very important data stored inside my system.please help me if you know how to solve this..... (HowTos)