I have a late 2010 iMac 21.5. I'm about to sell it so I wanted to reinstall Snow Leopard and restore the drive to it's original out of the box state. I've made a mess of things and now I cannot re-install Snow Leopard or even Lion. I'm left with 2 .dmg images that I cannot eject or close. I've tried erasing the drive and also setting up a new partition. No matter what the files have me locked up and the Mac just keeps repeating the pattern. How can I resolve this? Thanks