You could try a re-inclusion request. State your mysterious problem and just frankly ask why and if there are any penalties or what you need to do to start ranking. However Google do take forever to do anything. And even if you are doing the right things already you may only see results in a matter of several weeks.

Re-inclusion requests here (pretty much your only way to ask Google anything easily, but responses aren't guaranteed) https://www.google.com/webmasters/tools/reconsideration?pli=...

Or try the Webmaster forums, where Google folk apparently post every once in a while, but it's mainly a clusterfuck of people hijacking your problem with their own questions, and solutions being unreliably crowdsourced.

Remember: Google moves in mysterious ways. We cannot understand their arcane techniques for we are not worthy.