After you installed the game it should work, otherwise you're suffering from a bug.
Actually, it would be good to note that if it's not there, try validating your Steam files. That should update it, and bring you to Wrath of the Lamb. Of course, you also need to buy it first.
yea same here guy on the top not doomspeaker but the guy above him it no activate and for the guy above me= ????
What do you think DLC means?
Once the DLC is activated, is it possible to switch between regular play and extended play? Or is the change permanent?
Permanent
There's a custom launcher out there that can allow you to play without wotl, though.
Download it on the free full version, or buy it on Steam. The game should work regularly or normally if you getting an recomended system.