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Here's the gen/md 3-country mod diagram.
the Mega Drive automaticly defaults to cartridge play when one is inserted, It's how the hardware is designed.
so this is why you can't get it to play your games.
In order to play Mega cd games, set the region switch on your mega drive to the region of Mega/Sega CD you are using, (i'm assuming it's EUR) and make sure you Don't have a cartridge in the slot, then it should work just fine. 
Like I said before, you still can't play import Mega CD games, unless you were to connect a Japan or USA CD system to your mega drive. The mod you did has little effect on the Mega CD's abilities, you'd have to mod it separately.
You could get one of the converter carts or a multibios if you want to use use import CD's on your existing Mega CD. |