If you didn't get a Windows Installation Disc when you purchased your computer, aside from spending Hundreds of dollars on a new Version of Windows your only option is repairing/recovering your existing copy of Windows.
With this disc, you will have the same tools used by a lot of computer technicians to recover a broken Windows installation. It provides you with the option of repairing your system (searches for problems and attempts to fix them automatically), rolling back to a previous system restore point, recovering a full PC backup if one exists on your PC. You can re-install to new condition using your existing key code and Windows Image.
What it does: The Windows 7 Recovery Disc can be used to access a system recovery menu, giving you options of using System Restore, Complete PC Backup, automated system repair, and a command-line prompt for manual advanced recovery.
What it doesn't do: You cannot use the Windows 7 Recovery Disc to re-install Windows.