I have used elements in the past on my pc, but just got a imac and downloaded the ap version of elements and am having trouble importing the video. I have clicked on add media files and it says to use the video importer. When I go to the video importer it says it can't find a source.
That would indicate an issue with your Mac recognizing the external drive.
Can you import the video if you move the media to your internal hard drive? If so, it's an issue with your system configuration.
I use an external drive as the media drive on my Mac with no issues whatsoever.
Welcome to the forum.
Like Steve, I use external HDD's, though on my PC. This ARTICLE goes into a few more details, though it was written with the PC in mind (back then, PrE was not yet ported to the Mac), and there are going to be a few system considerations, regarding "mounting" externals, that will be Mac-centric.
Good luck, and please report on Steve's suggested test of Copying your files to the internal HDD, and Importing/Get Media from there.