System Restore is a component or feature of Windows XP, Windows Vista, and Windows 7. In Windows Vista, Shadow technology is used to create restore points. If a computer becomes unstable while downloading games or a software due to a virus attack or any other reason, this feature can resolve the problem by taking the computer back to a prior check point. In case of a system failure, it provides you an opportunity to roll back the registry keys and system files to a previous check point. It performs a vital function of saving snapshots or restore points of your system settings and files. It creates restore points on its own, if there's a significant change in the file or application structure. Problems can arise if System Restore does not work. Reasons At times, this feature does not work in Windows Vista, Windows XP, or Windows 7 because of insufficient hard disk space. At least 200 MB of free hard disk space is required for it to function properly. This space is required for storing the data gathered for the restore points. If the disk space is less, this feature will be disabled. Once the space required for the data is available, it will start saving and creating the restore points until this space is full. When all the space gets used up, it starts overwriting, starting with the most recent data. Another reason why this feature might not work could be a virus attack. Sometimes, restore points get corrupted due to computer viruses or an anti-virus software. So, make sure that you are using an effective anti-virus program. How to Solve this Problem This feature gets disabled either due to a lack of disk space or due to registry changes made by certain viruses. In case, this feature doesn't work when you boot normally, you can try to restore your computer in safe mode. To boot in Safe Mode, tap the F8 button while your PC is booting up. Once you select the option that allows you to start your computer in Safe Mode, check if this feature is working. At times, this feature might not work in safe mode also. Under such circumstances, the best option would be to use the System Restore disk. If you have this disk in your optical drive when your computer boots, the computer must boot to the restore disk, and not to your hard drive. You will need to make some adjustments in the BIOS (Basic Input/Output Settings) so that your computer boots from the restore disk. This will lead you to System Restore disk menu. Follow the instructions to use this feature. In case this feature is not working in Windows XP, you can boot your system from your Windows XP CD. To boot from the CD drive, make adjustments to BIOS. Put the XP CD in the drive and restart your computer. Once your computer boots up, you need to look for 'Automated System Recovery' at the screen. A scan will start and this program will find the required files from your XP CD. You will have to reboot your computer. After the reconfiguration of the system files, this feature should start working again. If this feature doesn't work, do a disk cleanup, check the antivirus software, or follow the aforementioned instructions to solve the problem.