If you ever need the Install DVD with SP1 included, go to the link and download.
Link has been changed....
When you try a startup repair, exactly what happens? Normally, you might see a message about repairing something with a reboot suggested. The first time you can agree, but if it happens again, ignore it and continue with the repair. If it says it cannot find an install, go ahead anyway.
There may be many different types of causes, but if you are not getting any bootmgr missing errors or OS missing errors, that part is probably OK. When it gets all the way to the Starting Windows and Logo, it is usually some type of driver situation. Have you installed anything new?
Some updates were just done probably today... those could be related. But the reason we start in safe mode is the system starts in a basic mode. Third party drivers are not loaded, so if that doesn't work, it seems it would be caused by an essential part of the install.
Right now, if you cannot think of a new device or a driver that was added for it, all I might suggest is you boot to the install DVD and run a chkdsk and a system file check from the offline state. Maybe that would correct something and allow you to get back into Windows. How to Run the System File Checker (Sfc.exe) Offline in Windows 7 and Vista - The Winhelponline Blog