Downloaded videos & music cant play

I can't play downloaded videos and music in the internet on my laptop (DELL latitude E5450, windows 10). Every time I play it on windows media player/Movies & TV and MP4 player, there's always an error. It says "CAN'T PLAY, THE ITEM IS MISSING OR WE CANT GET TO IT..0x80070002..I checked the properties of the file under "security", it always says again, "the requested security information either unavailable or cant be displayed". Anyways, all the videos and music are free download from youtube, pexels, etc. But when I watch it on my cellphone, I can see the videos and listen the music...only my laptop can't. Please help me settle above issues mentioned. Your help is much appreciated. Thank you very much.