A couple of weeks ago, a component on Hubble failed (read that link for the back story here). This critical piece of hardware controls almost all the scientific instruments on the observatory, so Hubble has been essentially down for weeks.
However, NASA anticipates such things, and when Hubble was built, all critical systems had a redundant set installed. In other words, there is another of these controllers on Hubble, but it's been switched off since just before launch back in April 1990.
Tomorrow, NASA will start the procedure to turn it back on. This process is tricky, as it involves basically shutting everything down, then restarting it again. It means powering up a piece of hardware that's had 18 years of napping. And it means several days of painstaking engineering and control, and making sure everything goes according to plan.
It's entirely possible that Hubble will be up and running by Friday, which is good. The Shuttle mission that was going to service Hubble (installing two cameras and a bunch of other needed parts) has been postponed until next year. They are considering bringing up another controller to replace the dead one; that's just in case the redundant one breaks down as well (and if they can't turn on the redundant one, they'll have to bring one up anyway). Ironically, the launch date was supposed to have been today, but now it won't be until February at the earliest.
NASA takes Hubble pretty seriously; in many ways it represents NASA itself. I'm glad. Hubble still has many years of peering into the universe ahead of it.
Oh, and if anyone at NASA is reading this: I went to the main NASA site. I went to the Goddard site. And as of the time of this writing, I found no mention of this anywhere, even though the telecon about it was 7 hours ago. On the NASA Hubble page, the last update was from two weeks ago. Maybe I missed it, but news like this should really be on the front page.