Well from what I've read on their site, when they get a ton of questions, they close up their ask, so if you want to ask something, you have to catch them when their ask is open, and as I don't know what time zone they're in, or when they open it up, I don't know when that is.
Also though...I found another Ask A Death Eater site that's relatively new, I think....you could try them......
askthedeatheaters.tumblr.com
and here's a link to the original one I think you're talking about:
