That does not work on such an old computer. Press down the Power button until the computer shuts down and then wait a minute or two. You will need a boot DVD like the one that came with the computer. Insert it into the disc drive. Press the Power button and at the chime hold down the "C" key while gently pushing the DVD into the optical drive until it catches. The computer should begin to boot from the DVD. When it does you will need to select a language. Wait until the screen's menubar appears at the top. From the Utilities folder select Disk Utility. After Disk Utility loads select your indented volume entry from the list on the left, then click on the Erase tab on the right panel. Set the Format type to Mac OS Extended, Journaled then click on the Erase button. When the volume has been erased quit Disk Utility and return to the installer. In the following screen select your Destination volume. Continue until the installation begins.