The charcoal in my BBQ seems to have stopped burning, what now?

So I'm using lump charcoal to BBQ a whole chicken. The coals were going nicely, covered with white ash and glowey and all that good stuff. Now an hour into it, there's some charcoal that obviously isn't burning, and just some that is. The stuff that hasn't burned yet doesn't really look like it's going to. I scooted things around a little, but I'm not sure what else to do. Someone else know more about grilling than me?