After reading over your first post, you stated
My dad was using the laptop, trying to configure and old printer connected to another PC with windows XP
If you are truly using Homegroup, the Windows 7 machine can only connect to other Windows 7 machines. That's it, no other OS.
When you ran the Take Ownership registry file, did it say successful or did it produce an error?
You could also try right-clicking on any folder, choose properties, click the Security tab, click Edit, select your username and give yourself Full Control.