I asked a question on SO some time ago and none of the answers were appropriate.
The question is effectively dead, but it affects my 'accept' rate negatively.
What should I do?
You should not accept an answer if you don't think any of the answers sufficiently answer the question.
I don't think there's a whole lot more to it than that. The accept rate isn't all that important.
I'm not sure if this is a valid solution, but...
Since you can always undo the "correct" answer and select a different one, maybe you could post a CW answer saying "There is currently no suitable answer to my question" and accept that, and then if a real answer comes along you can undo and re-accept that.
This means your 'accept rate' isn't penalised for a failure to find a solution, but unfortunately has the side effect of making your question look answered, and thus may not attract so many people trying to solve it.