Windows 7 Login Problem.

I have restarted my notebook (Windows 7), but now I cant enter anymore.

Whenever I get to the Login screen, it plays a sound, then the screen turns black, then it goes normal again, then black, and normal, as an infinite loop..

I can enter safe mod with no problems though.

So you did not install any updates or drivers or programs and you did not mess with the hardware in any way:
In that case, back up your data and reinstall.