If you didn't then you have not set the boot order to Optical Drive first.
Can you actually use any disc in the Optical Drive with Windows open? If you can not then the most likely thing is that the Optical Drive has failed. This is a fairly common occurrence if Discs are left in the optical dive when it is not being used.
Can the computer see the OS Recovery/Install Disc with Windows open? If the drive is working but you are unable to see this disc it could be damaged or just dirty on the Data Side.
Is this a Factory Made Disc or a Recorded Disc? If it is a Recorded disc it is possible that the Dye is not compatible with the Optical Drive.
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