Hard to say without seeing the aircraft.cfg file.

I assume the folder is still intact.

If you want to post the first few paragraphs of your aircraft.cfg (down to and including the General section) or email me the whole thing (just the aircraft.cfg file) I'll be glad to take a look at it.

Try this, too, although it won't fix your problem.  Start FS and look under Aircraft/Unspecified.  It should show up in there.