Hi
Not sure wheter the question is that you cant open the folder in whch the file is kept, or that the actual video wont play.
if it's the former, open "My Computer" and then click on the name of the pen drive. If you cant see the pen drive, try taking it out and putting it back in again, or try on a mates computer.
if it wont play, you probably dont have the right 'plugin'. Try downloading quicktime to your computer from http://www.apple.com/quicktime/ (it's free) and try again.
Richard
October 2008