if there is a cached pages, your site is not banned. if your site has no cached pages, your site is so new or banned.
my site also got banned one or two sites that were linking to my site and google emailed me about the sites and removed my site from index.
when i search the URL my site is show, so it's not banned, but when i search for keywords reliated with my site sometimes it shown at pages 48-52 and sometimes doesn't show. 3 days ago it showed at second page. does top sites cause this? i add some early.
It's very weird that, but if it's indexed its not banned dont worry, just work on your keywords, when getting back links target websites with the same keywords/content , and also use your link anchor which is the keyword your targetting, dont always use the same keyword on the anchor, rotate them