Snow Leopard’s been freezing (I can see the spinning ball all the time -one minute or more-, but can't get any reaction form any software) for years until I typed in terminal this:
sudo systemsetup -setkernelbootarchitecture x86_64
Snow Leopard can freeze in macbooks pro with leopard previously installed.
http://classictutorials.com/2010/08/snow-leopard-freezes-or-application-hangs-in-snow-leopard/
manoftherambla 