I assume you used Windows Encrypting File System. If you did not back up the Recovery Agent Certificate then I'm afraid they are gone for good. When you reformatted your drive Windows would have created new security identifiers (SID's) for each user, even if the users are identical. Therefore the files cannot be accessed, even by the admin account. There is no "back door" option to get at encrypted files.
It really is essential to back up the Agent Cert if you use file encryption.