On StackExchange Q/A sites this scenario has been questioned and answered on many ways. I don't believe deleting the questions should be the solution. Maybe in a near future some other new user know the answer to that question. Or, keep reading below the following links.

Some samples:

• How do I get attention for old, unanswered questions?
• How to get your questions answered?
• OK, Now Define “Answered”

And quoting one of the more accepted answers on this situation:

You can "bump" your thread by editing the question to provide status and progress updates resulting from your own continued efforts to answer the question yourself. I usually do that unless I really hit a dead end with no further clues to follow. Some times I eventually bring about enough understanding to realise the answer, and thus post a resolution to my own problem.

Other propossal is to add a "bounty" to the best answer. But I don't know if AskBot has this option. If available, here is another way:

If you have at least 75 rep points, you can offer a bounty, promising to give some of your points to the person who correctly answers your question.