I didn't mention this before because I thought it may be to complicated for you, and a Repair or Custom installation seemed more practical. Just go thrugh it a few times before applying, it just may be the solution to repairing the registry.
Read the linked article for propper instructions relative to this comment. The registry backs up restore files you may be able to use and restore the registry manually. Said files are in C:\ WINDOWS\system32\config. You can find several registry backups by sections, the question would be which section of the registry is damaged (probably System) so you’ll know exactly which registry backup file to merge to and restore the Registry. This Config folder is probably where the application I mentioned previously (RegResWiz) gets the Registry restore points, but why the application didn’t find any when you tried it, may depend on the Windows 7 strict security.
So, there is still a possibility of restoring the backup in the Config folder to the registry, but since these backups are in code, they can’t be merged directly into the registry.. a registry application is needed, or possibly the registry itself can make use of those backups. See if the following works:
Accessing the registry remotely from the Hirens CD, or a new intallation, select the HKEY_LOCAL_MACHINE hive, next to to File Menu > click on Load Hive > browse to C\Windows\System32\Config\ > select the file named "System" with the creation/restore date thats most convenient > name the new registry key as “AAAA” next “Export” AAAA” with right click Export.. this will convert the key from system (without format and in code) to a .reg edit file that you can "merge" into the registry… Next right click on HKEY_LOCAL_MACHINE and click Export > name the Exported backup.. Next rename the HKEY_LOCAL_MACHINE hive to OBSOLETE > next rename the key you named AAAA to HKEY_LOCAL_MACHINE.. This may replace the Local Machine registry Hive with the saved backup (in C:\WINDOWS\System32\Config\"System" with convenient date of creation).
It's possible you may need the application mentioned in the link, named RegFileExport v1.06. but this application is made to work remotely from a network not from a Live CD, but it's worth downloading it to drive C:\ and trying to execute it from the Hirens Boot CD.
If this concludes successfully, see if the Windows 7 on C:\ now boots.. if it works, go into the Registry and delete the key you renamed to OBSOLETE.. if it doesn't work, go back to the Hirens Boot CD access the C:Win 7 Registry and delete the Key you renamed HKEY_LOCAL_MACHINE and rename the OBSOLETE key to HKEY_LOCAL_MACHINE.
How to Restore Previous Versions of the Registry in Windows 7
http://www.howtogeek.com/howto/31136/how-to-restore-previous-versions-of-the-registry-in-windows-7/
RegFileExport v1.06
http://www.nirsoft.net/utils/registry_file_offline_export.html