upgrade - Caught in login loop after upgrading to Ubuntu 14.04, can't login to the root either

I am totally new to Ubuntu which came pre-installed in my laptop. I upgraded to 14.04 version but I think it was not installed properly when I restarted the system. Now it is not letting me login even though I am entering the right password. I read somewhere to enter into root but I can't as I don't get any screen on pressing Alt+CRTL+F1 or F3.