Since the Win 7 (64 bit version) is encountering some problems, I would like to know which critical files (and where I might find them) I would need to Restore a 64 bit version of Windows 7?

   The registry files are what is needed.  Most of them are found in the Windows\system32\config directory and are the files that do not have an extension to them, for example, "system".  There are also some user files in other locations.  If you do a registry backup using RegVac and open the user.ini file in the registry.daz file (which is a zip file) in the backup, it will tell where the registry files are located.
   These files cannot be restored while Windows is running because they are locked open to protect you from such a thing accidently happening.  Windows comes with a procedure that programmers can use to restore the registry, but in Win 7 64 bit that procedure does not work properly and ends up crashing the computer.
   From outside of Windows all you need to do is copy good registry files into their proper directory.