Sadly, from personal experience if SP1 doesn't install, let's say 95% chance you will never get it to install except for a complete reinstall of the OS.
I've spent many, many, many wasted hours trying everything suggested everywhere across the internet on a wide range of machines that had service pack update problems, and it rarely works, in fact I cannot think of a single time I've gotten a troubleshooting advice to work installing a service pack on Windows 7 where it wouldn't before.
Most recent machine I had to do a complete reinstall, for some reason all updates that did not require a reboot installed fine, but all that required a reboot failed. Tried everything, including an in-place upgrade of the OS. Nothing worked. Was forced to save the data, format the drive, and start from a fresh install.