So, about a month ago I switched from my old windows 7 computer to a windows 10. I had used the exact same program on an ongoing project for a few weeks, and moved it onto an external hard-drive. But once I tried to open it again, I got an error message, saying "This type of file is not supported, or the required codec is not installed."
It's a .avi file, and I know it is supported because it was reading the file just fine on the other computer, so that leaves the codec. But I have no idea what that means. Help?
Your old computer must have had a codec installed that your new computer does not. If this were a standard DV-AVI, it's pretty likely that codec was either already loaded onto your operating system or installed as soon as you installed Premiere Elements.
But AVIs can be made up of any of thousands of codecs.
Open this AVI in the free download MediaInfo. In MediaInfo, set View to Text and then copy and paste that report to this forum. Once we know what the file is made up of, we can better recommend how to proceed.