A common problem with new laptops is that Windows 8 or 10 is pre-installed. In case you want to install windows 7 or linux, the BIOS settings prevent to boot from CD or DVD. The same issue happens to lenovo G50.
Find below the BIOS settings that lets you boot from CD/DVD on G50. To enter BIOS press F2 while press the power on button
Secure Boot = Disabled
Boot Mode = Legacy
Boot Priority = Legacy First
OS Optimized Defaults = Other OS or Disabled