SysChat - Downloads (Freeware Utilities) - MS-DOS 7.10 CD Full Installation
There is no password on this .zip of DOS 7.1
Since you have the cd key, you could download a cop of the disc from somewhere and use your key. Owning a backup of any media you have purchased is legal, especially since you are using a legitimate cd key.
The problem could be any number of things, the restored orphan files may have had similar names to windows files and replaced them, but that is a long shot, it is possible something completely unrelated to all of this caused the issues as well.