black screen after the ubuntu logo shows up

[lilipop]

hello,
i get the following error:
https://www.youtube.com/watch?v=3Xf0_F7a8U8

so bassicaly when i try to run ubuntu, then the ubuntu logo shows up and after that i get a black screen for no reason, i dont know why ...
the windows runs normally.
so, what i should do?

thanks in advance for the help.

[lilipop]

ok, i think that this http://ubuntuforums.org/showthread.php?t=1613132
will help me. i will try that later and tell here something

[lilipop]

hello,
i have partially solved my problem but when i get to the login screen and i enter my password then the screen turns black and i get again to the login screen to enter my data.
the same happens to the guest sessio, when i just click to enter i get a black screen and after 1 second i get back to the login scree.
akward....