Do a search in google; http://www.mysite.com If you are banned - not any pages from your domain will show up there.
if you want to know in which search engine you have been banned then you need to search your URL in that search engine if it is not showing your site then you are possibly banned or not indexed by that search engine robots. use site:"www.xyz.com". query to know in google, yahoo and msn.
I can't see one of my sites in google.It was indexed before.but now its not seeing.My site was down for some days.But it works fine now. Is my site banned ? If banned what I can do ?
URL? Google gives obvious messages to the user when searching for the domain. Without the exact URL, nobody can help you.