A .MOV file that won't play on Windows is almost always a codec issue — MOV is Apple's QuickTime container, and Windows often can't decode the video inside it (especially HEVC from iPhones). The quickest fix is to convert the MOV to MP4, which Windows plays natively.
Why MOV files won't play on Windows
MOV is Apple's format, and iPhones increasingly record video as HEVC (H.265) inside it. Windows Media Player and many Windows apps can't decode HEVC without extra — sometimes paid — codec support, so the file opens to a black screen, no audio, or an error.
The fix: convert MOV to MP4
Convert MOV to MP4 (H.264) and Windows plays it with no extra software. It runs in your browser, so your video isn't uploaded anywhere — which matters for personal footage.
Why not just install a codec pack?
You can (for example, Microsoft's HEVC extension), but third-party "codec packs" are a well-known malware vector, and you'd have to install one on every PC that opens the file. Converting once fixes the file itself, so it plays everywhere without extra installs.
What if it still won't play after converting?
If the MP4 also fails, the original file may be corrupted — an interrupted AirDrop or transfer, for instance. Re-export or re-send it from the source. For the general approach, see why won't my video or audio file play.