This process involves having to reinstall the operating system using the Windows 7 installation media, and formatting, which will erase everything on the hard drive. You'll also need to reinstall all your applications once again, and use a backup to restore all of your files. This process takes more time than other methods, but it will ensure that everything works correctly.
1. Reboot your computer with Windows 7 installation files (make sure your PC is set to boot from the drive with installation files).
2. During the Windows Setup, click Next, accept the licensing, and click Next.
3. Click the option Custom: Install Windows only (Advanced) option to do a clean installation.
4. Delete any partition created by you current installation of Windows.
5. Select the empty drive and click Next to start the installation process.
Important: If you have a partition where you store files or a secondary hard drive, you don't have to delete these partitions.
Once the Windows Setup process completes, you will once again back to Windows 7. However, remember that you need to restore your files and reinstall and configure all the programs you have previously installed on your system.