how does your topic become lock & can u unlock it?

Multiple reasons but mainly if someone breaks the rules and or the topic breaks the rules...... much like this one. For further info PM a mod

A mod tells you why they locked the topic (usually because someone didnt read the forum rules, posted in the wrong place, or had no real topic).
And once locked, no you cant unlock it, or even start another thread about the locked topic.

I'm pretty sure your thread was locked due to it already being talked about or it should have been added to the "What do you want in New Vegas" thread, but a thread can be locked for a number of reasons. This will get locked because it isn't on topic or anyway relate to New Vegas. Usually if a mod feels it should be locked for a reason it will not likely be unlocked.

Well, a locked topic can be unlocked by a Moderator... but it doesn't normally happen (usually, if they temporary lock it, it's for "cleaning out" flamebait, trolls, etc. from the thread. Once cleaned, the thread may be unlocked at the moderator's whim.)

Also, a locked thread may be restarted as a new thread- so long as the lock was because of people being idiots, not because the thread itself broke forum rules.

You can PM a mod to ask questions if your thread was locked or a post deleted or what have you. However, in the rules (which you agreed to when you joined) we do ask that you do not start threads about locked threads, or repost a locked threads.

And Marss - a locked thread that was locked for causes like flaming, derailment, general shenanigans should not be restarted without asking a mod if it is okay. Threads that are locked because of post limit and such are fine to start another sequence.

Hope that clears up the mystery.