Does any other AVCHD file able to be played on that PC? If not, then that would point that AVCHD codec is missing on the PC and therefore the file is not able to be played. Please take a look below to know how can you install such missing codec.
In case all other files are playable then your files might got corrupted when renaming them. I would suggest to get back on your iMac and copy them into a different location (USB disk, etc.). Also you can check whether the files are repairable from your PC using MP4repair.org
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