Is there a video player on windows for iPhone recorded videos?
Let us assume your videos that you can't play back are in the .HEVC (.HEIF for images) format, which are not natively supported in Windows. Therefore, VLC should be able to playback those files. Is it up to date? 

To further address your issue, we need more info:


file format of the videos that don't and do playback?
Do they play on a different machine?
are the files showing black, or what is happening when you double-click click them/open them in VLC? Any error message?