One thing you can do is change the file extension from XLSX to ZIP, then browse the "subfiles".
It is a long shot, but you may be able to copy out the sheets and place them in to a new workbook via the same method.
P.S. I'm sure it's obvious now - but you really need to think about a backup strategy!!
Use the inbuilt utility that comes with excel application that is popularly known as Open and Repair
Click on Office button
Then click on Open
Now select your file
Now click on arrow located next to open button
Finally click on Open and Repair
Once you perform the above steps, a new dialogue box will get displayed which will inform you “Excel can perform checks while opening the workbook and attempt to repair any corruption it detects, or extract just the data (formulas and values) from the workbook”
You can click on Repair if earlier excel was not able to repair the sheet.
Or you can click on Extract Data if you want to recover data from it.
2 - Use Backup for restore
If you have created the backup then you recover your excel from there.
3 - Use Excel Repair and Recovery tool available over the net. Just Google it. You will definitely going to find appropriate tool that can fix your problem.