Hi,
I can't specifically state why your files did not successfully back up and restore. You may have had file encryption or other protective measures taken to sfaeguard them, which should have been removed before backing them up, and they are no longer accessible because of that factor. There may be a different reason.
The important point is, you should stop using the original hard drive IMMEDIATELY!
There is a high likelihood that your original files are still on the drive. They will not have been overwritten unless you have already stored lots and lots of new data on the drive. They will simply have had their 'signposts' removed so that Windows can no longer find them.
A professional Data Recovery Service will be able to recover any of your files which still remian intact, and such parts of other as remian there. If the data is crucially important for a court case, then I'm afraid that the rather high cost of such a service is the best and most sensible course of action available to you.