It looks like select Xbox Live services are currently down for owners of Windows 8.1 PCs trying to access the music and video stores. According to the Xbox support page, the service interruption is described as "limited" and affects "browsing the Xbox Video Store and Xbox Music Store" from your Windows 8.1 devices.
There's no need to worry, our team is aware and working toward a fix! Thanks for being patient during this process, Xbox members. We'll update you as soon as we have more information.
If you've experienced an interruption in service, visit the Xbox support page to monitor if Microsoft has restored Xbox service.