I've a 15" 2011 MacBook Pro, currently running El Capitan. I need to downgrade all the way down to Snow Leopard. The reason for this is that the sole reason I have the laptop is to run some video analysis software called Sportscode, and the version I have is only compatible with Snow Leopard. I have the original Snow Leopard Install disk. I've reformatted the Mac hard drive, so now it's not really running OS X. When I turn on the Mac and hold down the 'C' key to start up from a CD, it just loads endlessly. I left it for over 40 minutes trying to boot, but nothing happened. When I hold the 'option key' when booting, and open up OS X Utilities, there's the option of "Reinstall OS X", however I can only reinstall El Capitan. I'm just looking to do a clean install. Any tips or advice would be greatly appreciated. Thanks!