Seeing as no one else wants to help I will try using my crystal ball and fill in some blanks correct me if I get it wrong!
The Debian download was of the “squeeze” variety dated 19-04-12
Your SD card is between 4Gb and 16GB in size and is a class 6, to 10
OK so what’s happening?
The “code” you see on screen is actually readable text even though it is fast moving
Somewhere several lines up in this text is a mention of “mmc0: error-110” and another with another mention with “….failed to switch retrying…” I forget the exact words
A quick trip to Github to download updated firmware will help resolve this
Download the zip or tar file depending on which operating system you use to write your SD card and extract them to the boot section of your SD card so they replace the existing files and try again.