I'm guessing this still happens after closing, and re-opening Maya? Are you using dual-monitors? Pull the hypershade onto your main monitor, and exit Maya. Try opening it now. Sometimes it gets messed up if it's being dragged from one window to another, or starts on the non-primary monitor. Try disabling your second monitor (not just turn off) and see if the problem arises then.
Imagination is more important than knowledge.