Excel cannot open this file. The file might have been damaged or

I've had this twice now with the same spreadsheet (quite a large one)
and Excel has now irrevocably lost data for me. I have a version in
backup, but all is lost for what recent data  Excel 2008 has destroyed
in its mangling it seems. Older versions of Excel used to be able to
do data recovery, but I guess this is now impossible?

Before I go back to Office 2004 (which I intend to do), is there any
way to recover the data?

Oh ... and how does consumer law work in the US (where I bought the
software)? It's obviously not fit for purpose as UK consumer law would
understand it, but do I stand a chance of a refund?

Cheers,

Jon