You'll need to tell us what program and version of that program you're using. What program was the file made in? You also need to tell us what type of file you're trying to open. Have you tried opening the file in any other program that should be able to open that file type? And what OS are you using?
The staff at Adobe are pretty good at troubleshooting, but they can't figure out what's gone wrong if they don't know anything more than you've told us.