Using the file you downloaded, you have to make a bootable CD. Then you start the computer with the failed drive from that CD.
I am backing up two SQL 2012 databases with Retrospect v 7.7.620. Both reside on the same server. One database backs up fine. But each time I try to back up the other, it hangs part way. I have waited hours. The operations log says "Copying . . . ." The client says "In use . . . " I can turn the client off, and immediately the execution ends. The operations log says "Execution incomplete" but gives no indication of what the error was.