Having a disc in the drive will make no difference.

Reboot the mk3 and see if it starts working, you will know if it does as the menu screen will not look so mickey mouse.

BTW, you have a MK3 nav computer not a MK4 so you can only run a CD in it not a DVD,

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Sept 03, M3, Silver Grey. Retro-fits: Modded Mk4 DVD Drive, OEM Bluetooth, VR Control, Rainbow Speaker Upgrade, Sony SOT Amp, HK Sub, CCFL, Intravee II, NightMode.