Files display only ^@^@^@^@
File extensions can usually suggest the type of contents a file might have, however, sometimes files are misnamed, and sometimes files are corrupted.  I presume that if you're accustomed to opening filenames with a similar extension with a text editor like nano, you're expecting this file to be plain text as well.

Give the command 'file' a try; that could tell you what the contents are. 
Also, if it's mixed text and data, the command 'strings' can help pull out some interesting text in an otherwise unreadable (to the eye) file.