ok you probably figured this out yourself anyway but im gonna say it because im stoopid and cant think of anything else ok
and id also making another copy before trying the half assed useless suggestions i make
sorry i cant be more help 
the text/information is there, its just decided to change it into all that gobbldygook
have you tried
opening it with another application. try em all, word, access etc
formatting the cell/s to try and get a cell type that may show more info
i doubt a function will decepiher the text any better but you can try, there are lots of different types you can unlock not usually used
sticking one of the cells in a visual basic code (like adding 2 cells or sorting etc) andseein what happenes
re-saving the file as a more basic file type and seein if the data becomes readable

and id also making another copy before trying the half assed useless suggestions i make


the text/information is there, its just decided to change it into all that gobbldygook
have you tried
opening it with another application. try em all, word, access etc
formatting the cell/s to try and get a cell type that may show more info
i doubt a function will decepiher the text any better but you can try, there are lots of different types you can unlock not usually used
sticking one of the cells in a visual basic code (like adding 2 cells or sorting etc) andseein what happenes
re-saving the file as a more basic file type and seein if the data becomes readable