Same for me, I was about to ask the same thing. :/ Someone must've disabled the chat feature.
Admins decided to close it for a week due to troubles, and I think it was the right thing.
Please see User blog:ToaMeiko/Chat
I thing this is a hilariously silly attempt to solve the issue that about 5 people have, by inflicting a punishment on the whole community. If you want to stop those people who are ruining chat for everyone, just ban them for a week.
What do you think?