Zip files are not actually a form of image file, they are simply a compressed file or files, so even if the png files were turned into zip files, when you decompressed them, they would still be png files

What you can do is to convert the files using Preview if you are using mac (save as jpg). I don't know what you can do on windows, there maybe an equivalent to Preview where you can convert the files. Or if you pm the files I could convert them for you.

I don't know why the png files don't work, they should work on all operating systems maybe you haven't removed the numbers before the file names?