My computer: after i log in it shows a loading icon, on and off. I can't open anything...?

...not even the start menu. I cannot open Task Manager. When i try it goes to a Blank screen and it is frozen on that black screen. I can not even see a mouse cursor. At that point i just Hard power off. Any ideas on how to fix this? SONY VAIO Model: PCG-71C11L Windows 7 Home Premium