Have you re-booted your PC? That fixed about 90% of these kinds of problems..
If that doesn't work, maybe re-install WMP fresh?
Or perhaps go to "uninstall programs" and see if, when clicking WMP it shows an option to "repair" as well as uninstall.
If everything you try fails, you may be forced to "roll back" your PC to a time when WMP was working correctly. I don't have Windows 10, but if you left click "start" in the lower left hand corner and then type in "restore" you will probably see an entry for "restore system to an earlier time." Left click that and choose "open system restore." Then choose "next" and there should be a list of system restore points. You want to find one that shows a time that is before your WMP went bad, highlite that entry and choose "next" and it should be self-explanatory from there. Just make sure you don't roll it back too far, cuz although it will leave your own files alone (audio, video, folders, etc), it will uninstall any software or Windows Updates that were installed in the interim.
But before you put yourself through that, consider downloading a free and legal media player, at least to have as a backup if WMP fails. There's some really good ones out there that are constantly updated. I use the VLC Media Player, it's kind of ugly, with orange cones as icons, but it's a great piece of software.
If you do download it, be aware that in the process of installing it, you will hit "next" once or twice and then arrive at a menu of things you can leave alone or uncheck. If you don't want your file associations to change you can uncheck "audio files," and "video files" --but if you want the ability to just, say, click on your audio file and then have the VLC player play it, you'll need to leave at least the audio file associations alone. The audio files icons will change into orange cones, and you can just click your files to have VLC play them. If you don't want to have VLC associated with your audio files, uncheck "audio files" under file associations. Once installed, you will just need to drag your files into the VLC player for them to play, or browse for them with the player.
I don't have the latest version, and in my version they don't try to add a google tool bar or anything, but just read carefully if you arrive at another menu, before it's actually installing, recommending you add some tool bar or what not, and then make sure you set it so that it won't do that, either unchecking or checking a box, as the case may be.
This would take you to the download page. I don't think Brian would want me putting the actual .exe file here, but it will be the blue icon that says "download VLC." I've used it for three or four years. It's safe and plays every type of audio and video and is constantly updated, and is legally free.http://www.videolan.org/
Whatever you do, just go slow..
I hope something in here was helpful for you.