https://arstechnica.com/gadgets/2018/03/oculus-rift-runtime-service-error/

Oculus Rift users worldwide found today that their headsets stopped working completely. Users encountered a "Can't Reach Oculus runtime Service" error, which prevented further use of the headset. The problem appears to affect most, if not all, Oculus Rift headsets.

Users began reporting the issue in the Oculus forums, and Oculus tweeted an acknowledgment of the problem at 12:26 PM today, along with a link to a support forum post on the subject, which simply says the following: