Questions that have no answers and were not automatically deleted by Roomba might have a positive score and / or several comments preventing their deletion.
- If the comments are not helpful anymore, flag them.
- If an old comment has the answer and is helpful, post it as an answer to improve the visibility of the answer. Before doing this look at the corresponding per-site meta to see if the community prefers that these kind of answers be marked as Community Wiki or not.
Regarding reposting a question, despite the discussion about the ethics of that, please bear in mind that reposting a question is not allowed. You might improve the post or post a similar question if you are able to make it really better than the "original" i.e. you made a significant research effort and tried things that the "original" question doesn't mention.
Regarding questions having unaccepted answers, if the answers are helpful upvote them, if not, downvote them. If it's meh, then ignore them and if they are really bad or cause harm, flag them. If you have the close to delete privilege, vote to delete them.