Try recovering the File in FileMaker 7 before attempting the file conversion.
Look for backup copies that aren't damaged.
If all else fails, you can export the data from the .fp7 files as tab, csv or merge files and import the data into a new FileMaker 12 file. That doesn't convert over the design of your original files, but at least you are able to get your data into FileMaker 12.
Thanks the recovery worked
Thanks for your help