In my own thread here (it's long and detailed but you can skip to the bottom where i had resolved the non working DLC issues with The Old Gods etc):
http://forum.paradoxplaza.com/forum...solution-to-installing-GG-version-of-CKII-DLC
The solution was to make sure i was running in my Administrator profile and ensure CKII plus all installation actions were run 'as administrator', this then allowed my DLC to work in game (i.e. i could start at 878 AD(iirc), chose a Pagan(The Old Gods dlc) or Muslim(Sword of Islam) leader etc. Trying to get the DLC working in a non administrator profile (which is what i use for the internet in general for security reasons) would stop it working in game, even if you had them all ticked in the launch menu screen.
For my GG version of the game i also had to have the patch (1.10 was the one i tried, but maybe the previous one would work also?) active for The Old Gods dlc to work in game, and i had to 'reinstall' all the DLC via the in-game store (which if you get the greyed out buttons you have to do the uninstall stuff/remove that store.dll file thing etc).
If you are finding non of this applicable then as has been mentioned it is best to do a complete uninstall and remove all the Paradox stuff from the main 'C:\Paradox Interactive\Crusader Kings II' path (including all the parent folders in that) and the extra folder it will create on your PC, which depends on what windows version you are running (XP it is in 'My Documents\Paradox Interactive\Crusader Kings II', Vista it is in '(logged in Profile)\Documents\Paradox Interactive\Crusader Kings II' etc).
Once you have got rid of all remnants of the Crusader Kings II installation, when you do the complete reinstall you should get all your buttons active and functional again to complete the process properly. With a bit of luck!