Posting this here 'cause I don’t know where else to put it…
Maybe I’m just an idiot, but I’m pretty sure when I started using UnityAnswers it wasn’t using OpenID. I guess I’ve had a cookie resident for ages because I can’t remember the last time I had to enter any login credentials. Now it’s asking for an OpenID login. And I’m like, okay, OpenID is cool… but none of the listed OpenID providers are recognized as being associated with my account. So uh… I can’t log in to my account any more. All I can do is make a new one.
Am I missing something? 
you likely used the unity board login which no longer is present.
Meaning the account I’ve been using for quite a while now is just… dead, now? O_o
Following up for posterity, and for that one person who’s going to Google for this problem six months from now… 
I had one computer that still had a valid cookie, letting me access my original account. Account details indicate the account is unregistered; there was a helpful message to the effect of, “We only know who you are from your browser cookies.” Okay, that makes sense. I was able to associate an OpenID from there, and now all is well.