Hi again,
I think the moving of the post will be done by the friendly admins, but on the other hand it is good news that you got the bak file. Simply rename it to .tgd, that´s all. (maybe copy it before, just for safety)
I have no idea how often these are created and how much work you have lost, but that way you should at least get one version back!
Still it remains a mystery how you ended up with a completely empty file. Hopefully the same thing didn´t happen to the bak too.
Cheers,
J