What happens when you try to boot it normally ?

I second the above question!

Safe Mode loads a very basic driver and system file set. If you installed a driver that conflicts with Windows, when that driver starts to load Windows freezes, and you can't start the OS. But since only certain drivers are installed in Safe Mode and the conflicting drivers are not loaded it runs. Go into safe mode and then use System Restore to go back to a point before the problem started. System Restore sometimes lists the names of the programs loaded when it made the point, it can help you determine what went wrong. Usually loading new drivers without uninstalling the old, or using incorrect or corrupted drivers can cause this. If you know what driver is causing the issue, you can always stop it from loading at start-up from inside System Restore.