I have a biped in max and I imported the marine's bones and I was rigging him. I got him pretty much done and then when I went to edit the neck envelope I musta pressed something because now when I move one of the bones, the biped doesn't follow it :\ It did before, but now it acts like its not rigged, when it it.

You must have edited the vertices or a polygon/etc. because the skin modifier gets like that if you edit anything on the mesh. You'll have to redo the envelopes. (Make it an editable poly, that should wipe out the skin modifer and such. This normally works, but there's no guarantees on the matter. Then re-apply the skin modifer and redo the envelopes.)

All I did was manually change the abs effect on some of the verts. Anyways, I tried re-doing the whole thing, but I get the same problem.

Like I said, redsetting the modifiers doesn't always do it right away. Try a few more times and try to use editable mesh maybe. It'll work fine eventually.

Is the lightbulb on?

I believe so, although I don't remember. But it's fixed anyways thanks guys. Still want to know why it happens so I can avoid it later though.