You should be able to find what you're looking for in your
Boards folder. So it might look something like the following (
the one below I'm guessing is yours):
/cgi-bin/forum/yabb/board/BudgetEdited: tonyevans wrote on Mar 3
rd, 2013 at 5:45am:

Ah yes, yours is
/Boards/Stamp3.txt In that folder, just look for the board that has the thread that isn't responding, and replace it with a backup.
So if your board is named
Budget as it appears to be, then you'll be looking for a file named
Budget.txt to be replaced.
Before you do this, I recommend you first download an
extra copy of
Budget.txt in case it's needed. Be sure to upload your file as ASCII text.
By the way, you should be okay with that particular board/thread since there evidently hasn't been a post there since January 19th.
Hint: With backups it's good to have at least a 2nd and older backup in case you end up inadvertently backing up a corrupted file.
It's certainly overkill, but our forum usually has 4-5 backups at any given time (
we currently have 10 backups). There have been times, for instance, when I've had to retrieve a file from an older backup because a newer backup had the same corrupted file in it that was on the server. I don't remember having to go back farther than a 2nd backup, but you never know. An older backup might be needed.
By the way, have you run
Rebuild Message Index and
Recount Board Totals in
Maintenance Controls? That may be all that's needed.
Good luck!