Hi BB,
If you drag the window to the maximum size by the corners, that sometimes works. I think IE remembers the size of the last window opened, so if that was some sort of small pop up window, you may need to open a window, maximise it, then close and re-open IE, and it may remember the maximum sized window.
You could also locate the shortcut to IE in the IE folder, right click it, select Properties, then you can choose to open all windows maximised.