Problem with Mail in Snow Leopard

Well, this actually isn't about Snow Leopard, but I don't know where else to post this question because there's no longer a category for Mobile Me.

When they shut down Mobile Me, I received an email that said "if you want to keep your .mac or .me email address" do this. Whatever it was. I had to click on a link, or something. I did that. And everything was just fine.

But recently, I've been having a lot of connection issues, and today in my attempts to diagnose the problem, I was looking through Console where I noticed all the error messages MobileMe was generating because it was failing its sync. I thought, I don't need that any more, so I clicked on "sign out".

And, now, Mail can't connect to my .mac email account. I am locked out of it (apparently). I've tried signing back in, but no luck. I've noticed, when checking my account info in the preferences pane, the incoming mail server says "mail.me.com" but it is grayed out and I can't click in the box to do anything. All the other boxes are fine.

How do I get back into my .mac email?