Clean Install of Snow Leopard
Be sure to make a backup first because the following procedure will erase
the drive and everything on it.
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 DU 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, if supported), 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. When the installation has completed your computer will Restart into the Setup
Assistant. Be sure you configure your initial admin account with the exact same
username and password that you used on your old drive. After you finish Setup
Assistant will complete the installation after which you will be running a fresh
install of OS X. You can now begin the update process by opening Software
Update and installing all recommended updates to bring your installation current.
Download and install Mac OS X 10.6.8 Update Combo v1.1.
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
5. Wait for installer to finish loading.
ok i couldnt get pass step 1 i didnt have orrginal disk that came with it so i bought snow leopard from apple , so i heald down c after chime and it just went to apple screen and its stuck on that. now i tried holding down the c befor the chime and than after i held down option and my mouse popped up and a disk and it asked to install snow leopard i click on the arrown and than it sent me back to the apple screen. and umm side note i dont know if it matters but i added a 4 gig stick of ram and it origonally had 2x 2 gig sticks in it.....
Your iMac model is the same as mine. A late 2009, 27 inch screen model.
The original installed OS X version was either OS X Snow Leopard OS X 10.6.1 or 10.6.2.
The white retail OS X Snow Leopard DVD that the Apple Store sell has version OS X 10.6.3.
So, your iMac should boot this disc with no issue.
Try starting from the DVD, again and continue to hold down the C key until the iMac actually begins to boot and you see evidence of this on your iMac's screen.