Snow Leopard Clean Install
A Snow Leopard DVD may not work on a 2010 iMac. For example, according to everymac.com a iMac11,2 (21.5-inch, Mid-2010) came preinstalled with OS X 10.6.3. So, if your Snow Leopard DVD is OS X 10.6 then you should expect problems when booting.


  Note: While one may think 10.6 should be 10.6.0, doing so would differ from Apple conventions. For example, see an image of the Snow Leopard 10.6 DVD or the system requirements for the Mac OS X 10.6.8 Update Combo v1.1.