Q: can not boot to OS X Recovery to erase hard drive and re-install OS X early 2009 iMac El Capitan

You should do the following if you are selling it:

Before Selling or Giving Away Your Pre-Lion Mac

Follow these instructions until you get to Step 5:

          What to do before selling or giving away your Mac - Apple Support

When you reach Step 5 you will need your Snow Leopard or earlier installer disc that came with the computer when it was new.

1. Follow these steps for installing the original version of OS  that came with the computer.

     1. Boot the computer using the Snow Leopard Installer Disc or the Disc 1 that came

         with your computer.  Insert the disc into the optical drive and restart the computer.

         After the chime press and hold down the  "C" key.  Release the key when you see

         a small spinning gear appear below the dark gray Apple logo.

     2. After the installer loads select your language and click on the Continue

         button. When the menu bar appears select Disk Utility from the Utilities menu.

         After Disk Utility loads select the hard drive entry from the left side list (mfgr.'s ID and

         drive size.)  Click on the Partition tab in the DU main window.  Set the number of

         partitions to one (1) from the Partitions drop down menu, click on Options button

         and select GUID, click on OK, then set the format type to MacOS Extended

         (Journaled), then click on the Apply button.

     3. When the formatting has completed quit DU and return to the installer.  Proceed

         with the OS X installation and follow the directions included with the installer.

     4. If you are planning to sell or give your computer away, then do the following:

        After you reformat your hard drive and reinstall OS X, the computer restarts to a

        Welcome screen and asks you to choose a country or region. If you want to leave

        the Mac in an out-of-box state, don't continue with the setup of your system. Instead,

        press Command-Q to shut down the Mac. When the new owner turns on the Mac,

        the Setup Assistant will guide them through the setup process.

Then your optical drive has either failed or is out of alignment or your installer disc is dirty. Use a lint-free cloth and some regular rubbing alcohol to clean both surfaces of the DVD. Use a circular motion starting from the spindle hole and working out to the rim. Be sure you remove all dirt and smudges such as fingerprints. Then try it again. See if the disc will mount on the Desktop.

Booting From An OS X Installer Disc

1. Insert OS X Installer Disc into the optical drive.

  2. Restart the computer.

  3. Immediately after the chime press and hold down the "C" key.

  4. Release the key when the spinning gear below the dark gray Apple

      logo appears.

  5. Wait for installer to finish loading.

What version of OS X does that disc install? The Snow Leopard installer is not a PPC program.