A few months ago I had just finished an install, and all of a sudden the same thing happened. Power still on, but loss of DSL sync. So I get all frustrated, thinking it is bad equipment, or something I did wrong.
Then it dawned on me. I'd seen hydro crews working directly above the DSLAM a couple blocks over. A quick call to the test centre confirmed there was an outage. Saved me a bunch of time troubleshooting for nothing!
Authorized Service Provider (Contractor) for MTS Allstream. Any views expressed are my own.