problem reading/changing downloaded files

I have downloaded my website onto my hard drive, no problem, but when I open files through the "local browser" window, half the document is in that computer gobbledy gook (little squares, etc.) Yet strangely, when I print it out, it looks perfectly fine on the hard copy. How is this possible? What is the explanation/solution? How can I edit and reupload files I cannot read onscreen?

I notice that in the local browser window, my file extensions (should be .shtml) do not show. I don't know if that's supposed to happen or not. Please help!