Go into phpMyAdmin, look in the adminlog table, look at the most recent records, it'll say which account deleted the forums.
It's my account. But it wasn't me.
Best thing to do then would be to trace the IP and see if the location is of anyone you think may have done it.
We think the new mod might have done it.
PS: How do i start again. Do I reinstall MyBB or can I just add new categories and forums?