Problem with joining a guild
 

I received the 'help' window about my getting a guild invite. I couldn't find a way to accept it.

I asked /ooc and was told to click the accept button but no window had popped up. I moved all the windows on my screen to make sure they weren't occluding an invite window.

What should happen, and what may be happening?

In your options menu, check and see if you are auto-declining guild invites.

Do you have a non-default UI?

I'm using the standard Titanium UI.

The Accept Guild Invites option is yellow (so on). (I turned in off and on just in case.) I see no other option related to guild acceptance.