Rolling Back to a Stable State with System Restore
System Protection is a service that takes periodic snapshots of your system state, including information about user accounts, hardware and software settings, and files required for startup. At regular intervals (once per day, by default), and whenever particular kinds of changes to your system occur (such as the installation or removal of applications or drivers), System Protection creates a restore point. If your system becomes unstable, you can sometimes return it to stability by using System Restore to return to one of these restore points.
If you dual-boot Windows Vista with an earlier version of Windows, such as Windows XP, be aware that booting into the alternative operating system ...