System Restore periodically saves a Restore Point to provide a means of returning to a known-good configuration should something go wrong. Just about any time you install new software, a Restore Point is created. You can also manually create a Restore Point.
System Restore will undo programs and applications that have been installed since the Restore Point, but data files such as documents, spreadsheets or music MP3's will not be touched. So, your personal data should survive the restore, but you may have to reinstall any programs that had been installed after the Restore Point.
If you notice that your computer is acting slow, weird, bizarre, funky or any other way than the way it is intended to run, perhaps it has been infected or compromised in some way. Follow these steps to return it to its former glory: Click Start | All Programs | Accessories | System Tools | System Restore Choose Restore my computer to an earlier time and click Next Using the calendar, select a day and Restore Point that you want to return to and click Next Save your work and shut down any open programs. Click Next to confirm your wish to restore your computer to the designated Restore Point.
The computer will shut down and reboot, after doing some thinking and making some changes. When all is said and done, the computer will be restored to the state it was in at the designated Restore Point and all should be well.
To make sure you don't end right back where you started from, you should make sure that your antivirus, anti-spyware and other security software are installed and running and that they are up to date.
