I've experienced this problem a few times, the first, I panic-reinstalled Windows. The second, I found a solution.
So you boot Windows, Defraggler starts, then hangs at "pagefile.sys - 0%" for a long time.
Assuming you can't boot into safe mode, which would allow you to simply disable boot-time defrag, then you need to do something really quick, (or long, if you don't have the equipment lying around like me). Grab yourself a Ubuntu or similar Linux DVD with Live Mode capabilities (I used Ubuntu 13.10). Once in live mode, open the drive that contains your Windows installation and find that pesky pagefile.sys. Now delete or rename it. Reboot to Windows. Boot time defrag should flash by in 3 seconds and everything will be great.
