Cannot open - file format or file extension is not valid. Verify file not corrupted and that ext mat

[jburgin0421]

Had an excel file opened. Rebooted machine. Now excel file will not open. It says "Excel cannot open the file XXXXX because the file format or file extension is not valid. Verify that the file has not been corrupted and that the file extension matches the format of the file. 

Any suggestions?

Jody

[#2]

@jburgin0421 

This is my case:

"we found a problem with some content in 'file name.xlsx'. Do you want us to try to recover as much as we can? if you trust the source of this workbook, click. yes"
I click yes, then another error

"Excel cannot open the file 'file name.xlsx' because the file format or file extension is not valid. verify that the file has not been corrupted and that the file extension matches the format of the file."