I don't know, because you haven't provided nearly enough information to even begin troubleshooting this problem.
What exactly happens when you try and restore?
What error messages, if any, are presented to you?
Are you positive that the files your accountant sent to you are compatible with MYOB?
Do you need to unzip the files first?
What version of MYOB and Mac OS X are you using, and on what kind of Macintosh computer, with what specs (processor, RAM, etc.)?