chosstronaut
What are the properties of your .mp4 file?
Video compression
Audio compression
Frame Size
Frame Rate
Interlaced or Progressive
Pixel Aspect Ratio
Do you see any association (video vs no video in Premiere Elements) between those files that are accompanied by .THM files and those that are not? From what I have read, those .THM files are just for thumbnails.
http://www.goprofanatics.com/gopro-hd-hero3/3896-what-lrv-thm-gopro-files.html
Can you rename the file extension of one of the .THM files from .THM to .jpg and then import the .jpg into Premiere Elements so that you can view it?
More later.
ATR