Cant able to change my OS

Hi, I am using Acer Aspire 4736 laptop with windows 8 OS. For a period of few months i am trying to change my OS to windows 7 but my current operating system prevents booting any different OS installation CD other than windows 8. I came to know about UEFI after reading your thread. so i checked whether "secure boot option is enabled in my pc". From the result i came to know my PC does not...