Lost charts in 2007
 

I have just opened a few excel files that had a number of charts in them that
were saved as sheets. The charts are all gone. The sheet still exists and
the tab name is there but the chart itself has vanished. I tried recreating
the chart and it was successful so long as it was only an object in the sheet
i was working in. As soon as i asked it to be saved as a new sheet it
disappeared.
Can anyone tell me where they all could be hiding please?
--
Moops