The DLC is NOTactivating for me. I have *SPOILER* brought my character into the purifier, put in 216, watched the cinematic then get brought to the main menu. I continue my game and am brought back the to purifier, and repeat.

Why is this happening if the DLC is installed from the disc and is being played on the DLC disc itself?

If you have installed the second disk, did you make sure to activate the files in the Data section of the launcher?

How do I activate it?

You've received the messages in game for all the radio transmissions/level cap increase? If not, you may not have opened the FO3 launcher and selected "Data Files" and checked the boxes next to each of the esm/esp files. Of course if you have done both of these things I'm afraid I won't be of much help. :/

Check the autorun (when you put in disc 1 in the cd drive).

Thanks evilangel I finally got to the data files thing. The launcher thing wasnt loading up for me before for some reason but now it is. I can finally play the DLC.

Same issue I had a few days ago. Just got FO3 for the PC. Was told all sorts of [censored] about Windows Live and downloads. Messed around with all that and after several frustrating hours, found that data files things was all I needed.