This can typically happen if you've installed some third party programs and set them as default viewer for a particular file extension and then subsequently removed the programs and they failed to removed themselves from the registry.
Most of the time Windows 10 will use the default and native "Photos" app to open most still images (.jpg, .png. , etc), so you might start there by
Opening "Settings" -> "Apps" -> and from the left column select "Default apps" have a look at "Photo viewer" and see what is listed and change it as needed by simply clicking on it to get a list of available apps.
IF it is already selected you may want to try going back to the left column and choosing "Apps and features" scroll if needed and select (click) on "Microsoft Photos" then click the link that says "Advanced options"
Try the "Repair" and or "Reset" buttons from there and see if you can fix it.
Regarding "movie files" I generally use a third party application called VLC Media Player
https://www.videolan.org/vlc/
Download and install it and use that as your default viewer for vids.