Read the step-by-step instructions written by an IT pro in the how to: Perform A System Restore Manually When Windows Is Not Bootable
The windows System Restore Wizard can be extremely useful when you need to reverse changes or settings made to your computer that may be problematic. If the system can't boot normally, but you can get into safemode, you can still launch the wizard from there. But there are times your computer can be so corrupted that even safemode doesn't come up. This article describes how to perform a very rudimentary, low-level system restore manually (without the wizard), offline, and without the need for Windows to boot.