My computer keep staying on the Loading screen once booted up

Hello,
Well here is my problem, once I power on my computer it loads up the BIO where is gives me some options to boot up;
Safe Mode,
Safe Mode with Networking,
Safe Mode with Command Prompt,
Start with last know succesful startup,
Start Windows Normally.
I've tried them all but once I try with 'Start Windows normally' it goes to the Vista Loading screen and stays there for about 15 minutes then it goes to sleep mode and restarts it self.

When I got to Safe mode BIOS come up with the whole list of directory files ect, and then it just stops on the certain one and after it being there for about 15 minutes it restarts itself aswell.

Please help I'm really confused on how to fix it. :S