@gav83collins: To troubleshoot the issue, please try heading to Settings > Apps > Tap the 3 dots in the top right > Reset app preferences. Next time you attempt to open a media file, you will be prompted to choose a compatible app, which will become the default option when the action is successfully completed.
Furthermore, please press the Volume Down and Side buttons together for around 10 seconds until the phone restarts, as this will refresh the phone and resolve any software issues which might be a contributing factor. Don't worry, this won't affect your personal data or settings.
If the issue persists, please clarify what happens when you try to take a screenshot or open a media file e.g. do you get any error messages or notifications?
