Can someone fix my tcx files

Those files cannot be fixed. A lot of the data has been replaced with zero's. Sorry.

Any idea why that would have happened?

Thanks

Nothing specific but I have a few guesses. :D

I have read that riding under high voltage power lines can screw up the data but I have never seen the actual results.

Your computer could screw up the data when it downloads it. Just last night my wife complained to me that her laptop had a corupt file with those same odd zeros or O's, whatever they are, and it had an odd name and was obviously not made by her.

I would go thru every folder on your gps and remove every suspicious file.