There are positive and negative aspects to both physical and digital media on next gen consoles. One of the biggest boons for disc-based games is that they're predictable - you know what you're getting and what's happening as soon as you slide them into the console's disc drive.
That's the theory, at least, but a quick skim on the Xbox Support Forums shows that that isn't always the case, so I've put together a quick troubleshooting guide to the most common problems Xbox One users encounter when trying to load games, CDs, DVDs or Blu-rays.
For all disc-based problems, the first thing you should do is to confirm whether the issue is with the individual disc or if it could be a problem with the console as a whole. To do this, simply try a different disc. If it's a game that you're trying to get working, try a different game, a Blu-ray or a DVD. You could also try the same disc on a different Xbox One console, if you happen to have a second lying around. If you've done that and nothing's working, try ye old faithful power cycle (below) to see if that sorts anything out.
If that doesn't work, or if you ever hear a grinding noise when discs are trying to load, Xbox Support recommends that you send your console in for repair. To do that, go to the Xbox Online Service Center to register your device (if you haven't already) and request a repair.If you can play games but not Blu-rays, CDs or DVDs, make sure that the relevant app for that function is installed. There are a few ways you can do this, either by installing the app from Xbox home, inserting a disc and having the recommendation to install the app pop up, or to Bing "Blu-ray player app" and install it directly from the search results. If that doesn't work, you may want to double check that the disc and the console were both purchased from the same country or region. Check here for a list of supported regions and their region codes. Some movies are region-free, so these should play on any Xbox One console.
If you keep getting the (0x21) error code on your console, your disc may be in need of a quick wipe down with a soft, clean and "slightly damp" cloth, as recommended by Xbox Support. Be sure to hold the disc by the edges without touching the top or bottom surface. If it seem clear of smudges and scratches, Microsoft advises you to power cycle the console: hold down the power button for 5-10 seconds whilst it's on, let it shut down fully, wait 30 seconds, and then start it up again.Unofficially, some users on the Xbox Support forums found that re-installing their profile helped overcome a problem whereby they'd receive the above error message despite the fact their discs aren't actually scratched. To do this:
1. Go to the dashboard.
2. Select Settings.
3. Select Sign-in, Security, & Passkey.
4. Select Remove me from this Xbox.
5. Restart the console.
6. Log in with your email and password.
Another user claims that you can get discs to work by playing hide and seek with the disc drive. "I always noticed it spins for a few seconds then does this slight noise and stops, then a few moments later I get a please insert a disc Blu-ray or game and so on... well I make sure the disc is clean then I slide it in half way where it starts to take it in.... wait a moment then let it go." Apparently this method "works every time", but obviously it isn't an ideal way to operate - if you are getting persistent disc read problems, there may be nothing for it but to send the console in for a repair.
Another common disc read problem on Xbox One seems to occur when users attempt to install a game from a disc, and the installation process stalls at or near 0% indefinitely. To stop this from happening, disconnect from Xbox Live, install the game, and then reconnect to Xbox Live. To do that, simply unplug the Ethernet cable if you're on a wired connection, or select "Disconnect Wireless" from the Network sub-section of the console's Settings menu. Power cycle the console, let the game install as usual, then reconnect to Xbox Live.
Here's one more piece of advice that only seems obvious if you know it already - don't stand the console up vertically, but on a flat, stable and horizontal surface. Just because either orientation worked for the Xbox 360 doesn't mean the same is true of Xbox One - as the official Xbox Support site says, "the console is not designed to operate in the vertical orientation because it could affect disc drive performance." My brother found this out the hard way after sending two 'faulty' consoles back. It was only after I asked him how he had things set up that we figured out what the problem was. D'oh.
Have you had any disc-related problems with your own Xbox One? Let us know in the comments and we'll see if we can pull together to figure out a solution.