If you try to upgrade Windows 7 to Windows 8 by using an installer file that you burned to a DVD, the installation may not start. You might experience this issue if your computer uses the UEFI specification when it boots, and also if the installer on the DVD is a downloaded ISO (.iso) file. This is the file that you obtained from the Microsoft Store after you purchased a Windows 8 upgrade license.
This issue can occur because UEFI does not recognize the DVD as bootable media. If you are not sure whether your computer uses the UEFI specification, check with the manufacturer of your computer.