I have been using Premiere Elements 12 for about 5-6 months now and I haven't had any issue with it, I record video on my computer using OBS(Open Broadcaster Software)
I have also been using OBS for like 3 months, and if you used OBS before you would know that it can take up quite a bit of CPU if you don't have some settings enabled which I didn't know existed at the time, so I looked for something that would use my CPU since I have something from AMD, finally found something, I recorded like a 22 minute video when I tried putting it into Adobe Elements 12 it would only show up as audio, even though is clearly a mp4, so I did some testing and turned off the setting that would allow my AMD card to work and did a test and recorded a short clip and that worked even though they are both mp4, I asked on their forums and they said it was with the editor, how can I fix this?
MP4s come a wide variety of flavors, and your software may be creating it with non-standard and uneditable codecs.
Open one of your video files in Media Info (a free download) and post to this forum the resolution, frame rate, audio and video codecs and the codec writer it displays. We'll then be able to tell you if a file conversion will fix your issue or if it's better to edit it in a less sophisticated, more versatile editor like Windows MovieMaker