|Are you running Windows XP? Your specs say Windows 7.|
If you have the XP CD, insert it into the optical drive and reboot the computer. Depending on the make model of the computer, the system may automatically try and boot to the CD. If it doesn't, you'll have to go into the BIOS and set the CD/Optical drive as the first boot device.
Once you've saved those changes and the computer starts, it will read the CD. Just follow the screen prompts. If the Windows install is "Seen," you can repair it.