One question - one thread
A rule of thumb is to keep one question in one thread:
If you have a problem and want some help, start your own question-thread, even if your problem very much reminds of a problem someone else had 3 years ago. (If you revive an old thread with additional questions or remotely related information, risk is that someone will name this a "Zombie", a dead thread that starts "walking".)
In the same way, you'll upset people if you spawn several threads about the same question. This may make people spending time on answering a question that already was solved in the other thread. So, if you start more than one thread, try to direct everyone to one of them.
If your question has "dropped out of visibility" but you still need an answer, you may return it to the list of latest questions by adding a new comment, a "bump". But at the same time, think a moment, did you give enough input for other people to actually help you? Better than just a "People, I'm still looking" can be to add something you forgot to include the first time around.
(Copied from my post here: http://techrepublic.com.com/5208-1035-0.html?forumID=101&threadID=338485&messageID=3388910 )