Btw, I had the hard disk replaced previously
>because of this error.

Is it the same disk ?
Sounds like incomptability between the HD and the controller. Command.com isn't found because of the fat sector written incorrectly, I suppose. I had that with 2 different controllers and one disk : on a machine everything worked fine, on another one, though BIOS recognized the disk, Windows 95 did not start. I tried everything, like you.
No luck.