".fp5" so you are using FileMaker Pro 5.5?
Is the file you are opening named Users.fp5 or does it have a different name?
FileMaker versions older than FileMaker 7 could only store a single table in each file and thus a reasonably complex system could easily require dozens of files in order to contain the appropriate data. Look for a file named User.fp5. Make sure that it's name has not been changed and that it an enclosing folder name was not modified if it is not in the same folder as the first directory you opened.
It's possible that users.fp5 or the one you are opening was damaged during the power outage. If so, you may need to replace with back up copies in order to fix the problem.