The good news is that it sounds like the hardware is working.
The bad news is that it seems like the data on the drive is now bad. We obviously can't be sure at this point if the files are still there at all, but there is a good chance that the partition table is just bad.
And the really good news is that Knoppix has tools that can examine the disk and recreate the partition table. Two such tools (I have no idea why there are two tools to do this) are gpart and testcd. There are man pages that you can read for each (at a command prompt type
man gpart or
man testcd). So far I've only used gpart, but testcd looks simpler to use.
If Knoppix can't repair the partition table for you, don't give up quite yet. There are other live CDs that have tools to pull data off such drives. One is
Helix.
If you post back it would be helpful to have more information about what you think was on that disk. Important information would include what OS your brother was running and what type of partition or partitions it should have. Information about what was happening when it stopped working may be helpful too.