I don't know what exactly caused this problem. I had the game up at the log in screen, but had not logged in yet. I left the computer, it went to sleep. When I woke it up, the main screen (with the chat window and army tab and stuff) was all black, but the login window was still visible and active. After logging in, the main window remained black. Probably not a big deal, but when this game goes double platinum you will have about 100 doofuses (doofi? what is the plural of doofus?) an hour calling tech support because they left the game like a doofus instead of playing it.

BTW, maximizing the window made it come back. Minimizing didn't affect it, and neither did moving it. Hope that helps.