If this m4a is from iTunes, then it's got heavy copy protection that keeps it from being used in a video editing project. That's why you're getting an error when you try to use it.
The solution is to convert the song to a WAV file using the free download Audacity.
As for the image or video that won't play -- well, we'll need more information. Like if you've got Quicktime installed, per the program's requirements.
Is your photos sized to no larger than 2500x1875 pixels (72 ppi)?
What model of camcorder is your video from and what format and resolution is it?
The m4a is Garage Band and I converted it to a WAV and would import but it still wouldn't play. I also tested MP3 files I had used last week. They will import but won't play. Quicktime is installed. As far as the source, I am just using images and videos from my iPhone 6 plus, like I've been doing thus far without issue. I am not using previously rendered video or images. Other video plays when I'm using other programs. I can play the vidoes that I've made previously with Elements, but not in the Elements work space. I can make an instant movie and the computer will generate it and render it, but it won't play.
You've got a slower processor, but you should have enough power to do some basic editing. Particularly if you're using MP4s for video and WAV for audio.
I assume you've also run Disk Cleanup and Disk Defragmenter to clear off a good 50 or more gigs of free, clean space on your hard drive.
In any event, you should definitely not be getting a generic importer error when using a WAV file or MP4 on a Windows 10 computer with Quicktime installed. But I'm not able to see why this is happening, based on the information you've provided.
Yes, I've got 64.7 gigs free, I ran disk cleanup and I've cleared the cache.
I may just have to re-install the program.
Thanks for your help, though! I appreciate it!