According to Oculus' website, the company had "an issue with our software certification that we're still actively working on". Until then Oculus Rift owners will have to settle for plain old boring regular reality.
One possible explanation for this problem is that an Oculus security certificate expired today. The only way to fix this is for Oculus to release an updated version of OculusAppFramework.dll with a new certificate.
"We're aware of an issue impacting people's ability to use Rift's software, and we're working to fix the problem", the company tweeted Wednesday morning. "Our teams apologise for any inconvenience this may be causing you and appreciate your patience while we work on a resolution".
Yesterday, they announced problems with the Nvidia driver updates that were effecting VR users. Some users have even resorted to changing the Windows 10 clock to before the certificate's date of expiration, although this temporary workaround could cause issues with Windows Update Service and is NOT recommended.