HI Experts

I am working in a start-up company in IIT-Madras. We are
running Rural -BPO's .Recently our people in Rural Areas faced a
problem in reopening the excel file , in which they were
working ,after power failure .

Full Senario

People used to work in Excel for continuous two or three
days(in the same excel file) .At one time ,there was a power failure
(They had no ups). They used to save the excel file for each row .Once
the power comes and when they try to open the excel file in which they
were working says file is invalid or file is corrupt....No Data can be
recovered ..

Can any one say how the file can be recovered or what is the
problem ,how it can be resolved