I asked a question on Stack Overflow, and got an answer, but when I tried the answer, it didn't help. Now the question is old and not getting any more views or answers, even after editing the original question to reflect that the answer wasn't helping. Should I post the question again, or let the question die and start looking elsewhere for help?
You definitely don't want to re-post the question. It'll likely get closed as a duplicate of the original. From the StackOverflow FAQ:
Editing the original will bump it. And the more information you can put into the question regarding your ongoing effort, the more attention it will get. Even if the only active person on that question "thread" is you, activity bumps it up.
The main thing is to make sure the question is clear, provides relevant information (no more, no less), and demonstrates that you've put in effort to try to solve it and truly hit a puzzling impasse.
If the only answer is incorrect, note that in a comment to the answer. And make sure the be clear as to why it's not working. Is the answer upvoted by others? Maybe it's not entirely incorrect but just isn't solving the problem the way your situation needs it solved? I've seen very long comment threads narrowing down that kind of scope.
No, but you can ask a different question about the same problem, I have been known to ask 3 or 4 question about different possible solutions to the same problem, with each question aimed that people that know about each of the possible solutions (and tagged as such).