When a file is deleted off the hard drive, the space it occupied is marked as "free", and the file will exist until more disk write activity re-uses the free space that it used to occupy.
If the files were deleted some time ago (and that sounds as if it is the case from your post) the chances of that disk space still containing the file are probably quite low.
If any part of the file has been written over, then it has essentially gone, unless you want to pay a lot of money to a forensic recovery company.
How important were the files? If they were very important then immediately cease using the computer, as every operation will reduce the chances of recovery. There is data recovery software available, but you need to slave the existing hard drive to another PC, as loading the software and recovering any file on the same disk could overwrite any other file yet to be recovered.