If your .xls workbook is corruprt you could try recovering it using the tools from the following microsofts Technet link. http://office.microsoft.com/en-us/ork2000/HA011383071033.aspx?pid=CH011494871033
If your not aware of the Microsoft Technet its basicly where all IT engineers look when they don't know the answer...which is a lot of the time believe me.
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix backup.