Reddit have started deprecating old.reddit.com as of a week or so ago, see: <https://news.ycombinator.com/item?id=49005747>.

The site still works if 1) you are logged in or 2) you're in the control of the A/B test group (presuming the A/B test is still ongoing).

I've been unable to access old.reddit.com for over a week now. Site's dead to me.