Hi Susan, I completely understand how important those family videos are and I want to help you get them working.
The issue comes from the way Google Pixel names and saves certain videos, those with “PXL” in the filename are usually recorded in HDR and use a format called HEVC (H.265), which Windows apps don’t support by default.
The easiest fix is to add the HEVC Video Extensions from the Microsoft Store or use a player like VLC that supports this format out of the box.
If you’d rather convert them to a more common format, a free tool like HandBrake works well.
Before we go further, can you confirm if the videos are in MP4 format and whether they’re 4K HDR?
That will help me guide you with the best steps.
Regards,
Aron