|This works on Windows 7. |
Open up an explorer page and manually resize by dragging the corners to the edge of the screen to fill it.
Leave it open and open a brand new explorer page and drag the corners to the edge of the screen to fill it.
I always do this a third time although I'm not sure if it's necessary. Open an explorer page and manually resize.
Now close all of the explorer windows in the same order you opened them.
Try opening a brand new explorer page (only after all of the others have been closed) and it should open to a full screen. You should be able to resize this screen to the size you want.