Hi
This is an issue that has come up before - try searching for problems before posting - a lot of problems have been encountered by someone before and have been discussed and solved.
http://archicad-talk.graphisoft.com/viewtopic.php?printertopic=1&t=21356&start=0&postdays=0&postorde...
or search for "windows not showing" - there are a number of posts and responses.