Can't update my chart

6 months ago, in Excel 2007, I started a spreadsheet showing items bought and
their usage by staff (ie. tea, coffee, soap, etc) from Sept 09 through to Feb
10. It's a really simple little chart. Just now, I renamed my Feb document
as "Mar 10", added the new figures, and went to update the chart. But the
chart s absolutely lifeless - it won't react in any way whatsoever. I have
tried creating a new chart but that has exactly the same problem. It looks
like a painting! Any ideas what's gone wrong?