My photos got converted into .MYD, .MYI and .frm files

[KBharathan]

Over the years, I have stored my digital photographs in folders by date of shoot.

I'm finding that a whole bunch of these folders now no longer have .jpg files.  Instead, they have been replaced by one of three file formats. For example, a photo titled 20070314_3063.jpg has become 20070314_3063.MYD, 20070314_3064.jpg is now 20070314_3064.frm and 20070314_3065.jpg has become 20070314_3065.MYI.

These pictures were shot with a Nikon D200, and I do not recall if these were originally .jpg or in NEF format.  I have no idea of what these formats are, nor of just what happened to make these changes.  I used to run Photoshop 3 at the time on a PC running XP.  I have since replaced my PC with a Mac and transferred all my files over, though I still have the old PC (totally disconnected from the internet before XP was phased out)

Has anyone else had this problem?  Is there some way to convert them back into the format they were?

I've lost something like 20 or 30 folders of photographs.

Will much appreciate advice on this.  Thank you.

[Semaphoric]

Those extensions are for MySQL: MySQL which is a database program. Were you using any sort of asset management tools on your old PC?

[KBharathan]

No, I wasn't using any asset management tool.

[Test Screen Name]

Take a copy of one file. Rename it as a JPG. Does it open?

[KBharathan]

I did remember - after hitting send on my reply to you - that at some point there was some utility that converted .DNG files into .NEF files.  I think I used it for some purpose or the other, but have no memory at all of the details - where when why.  I wonder if that had anything to do with this problem.  As you can make out, I'm a novice on these issues, _and_ have a very bad memory.  With apologies for both.