How to reinstall Windows7.

• Restart computer and insert windows DVD.
• Click any key for boot with Windows DVD.
• Select suitable language, time and currency format and click "Next".
• In next window, click "install now" for reinstall windows7 operating system.
• Check "I accept license terms" if you wish to agree Microsoft license terms.
• Select "Upgrade" for reinstall Windows7 again.
• Then again, windows operation system files will replace so if there's a corrupted file it will automatically replace to new one. This will take 30 minutes.