An ounce of prevention is worth, what, a working version of your operating system? A few hours of a Windows reinstallation? All of your system's data? When it comes to dealing with issues with your desktop or laptop PC, apps that help you prevent problems before they occur are worth their file size in gold.
Let's start from the beginning. Something's gone cataclysmically wrong with your Windows operating system and your only choice is to either restore it back to its original settings -- potentially wiping your data, your record of program installations, or just generally making your hard drive's contents chaotic -- or wiping your drive and reinstalling Windows from scratch. Use Clonezilla to clone your primary hard drive's contents to a separate drive before you undertake this process, and you'll then be able to copy your critical files back once your reinstallation is complete.