Flicker...the only rules here are the ones posted as sticky's. Nevertheless, since many of us access the forum using the "read new" function...when you post on a dead thread, we end up wasting time on old posts trying to get the context for your new post...without realizing the thread is old. If everyone did this, a lot of time would be wasted and frustration ensues...along with harsh words to the offender.
There are appropriate times to ressurect an old thread and it is helpful to the rest of us if one starts such a reply with..."I realize this is a dead thread but....". That clues us in that we don't need to read what came before.
Most often however...it is best to go back to the subforum main page and just start a new thread.