Spreadsheet works in Excel2000 but not in 2003

[Sarah]

I created a spreadsheet in 2003 (including macros) but it suddenly stops
opening. I tried to undo the last bits of work I had done (went back to a
previously saved version that was working), but it still does not open.
However, it opens fine in 2000.

I need to get it working in 2003 as the spreadsheet is for others to use.
If anyone has any ideas I would be really grateful.

Thanks,

Sarah