I am posting a small tip here which will help many people to restore there system via dos. It happens that your system may fail to boot and you also cannot enter Safe Mode. But still through DOS we can run system restore. Run CMD and then type rstrui.exe and hit enter. You can see System Restore window on your screen. You can then use the same to restore your system. This would help you to get your older system back. It is helpful against virus infection and crashes. Second method that you can try is using Windows bootable disc. I am talking about Vista here. Just boot your system with that and then click on Repair. Then choose System Restore.