Excel navigation problem

[Annette Searle]

I am running Excel on Mac OSX. All OK until a week ago when I noticed couldn't navigate from cell to cell using arrow keys - just moves whole spreadsheet. Have I accidentally locked something? This happens on PC's if you use the scroll lock. I am PC user at work, Mac at home and still getting used to differences. Would appreciate any advice on how to fix this problem, as I can only navigate by mouse click from cell to cell which is very frustrating.