Well, first of all; these Forums have no PM system (it's been discussed at various times, with the same negative results).
Secondly, threads are generally locked because they either violate the AUP (which you were supposed to read when you signed up)....or one of the stickies at the top of each Board (which are rarely read by members).
Outside of that, I couldn't tell you; however, Mods are under no obligation to inform you as to why a thread was locked or deleted. That's just the way it is....occassionally a Mod will do so, however.
-Keith