It's really up to you. Locking/deleting duplicate threads is done to curtail spamming and prevent multiple discussions of a topic that can lead to duplicate advice, confusion, and congestion. Personally, I feel if the thread is dead (no responses are provided for two or so days after the thread has been bumped) it's OK to repost in another forum to see if you can receive an answer. Of course there are exceptions to that general thought, so just use your best judgement. As long as you're not spamming the boards, there shouldn't be a problem...the old thread may be locked so traffic is directed to the new thread, but that's about it.
Hope this helps,
in a forum is it ok to post in another forum,cause there's that duplcate post problem.