It's probably underneath another window, and you try moving all your windows around until you see it. However, it could be off screen. In that case, open your UI_character_server.INI file in a text editor (WordPad or Notepad will work), Find "[EQMainWnd]", under that, there will be some lines, change or add the following:
XPosWindowed=0
YPosWindowed=0
RestoreXPosWindowed=0
RestoreYPosWindowed=0
And save the file. Do this while not logged into that particular toon. When you log that toon back in, it will be in the upper-left hand corner of your window.
EDIT: If all else fails, you can always delete the UI_character_server.INI file, and re-position / bring up all the windows. But one or the other of the above should work.
Yther Ore.
Edited, Aug 14th 2010 3:03am by Yther