First, I would look to see if there is any code in the workbook.

If you don't know anything about VBA, take a look at this link

Second, you can select Ctrl + A which will select the entire spreadsheet, then right click on the row headings and select row height. Add in a row height such as 15 and select OK.

Third, copy and paste all of your data to a new spreadsheet as text a format as needed. Maybe the spreadsheet is corrupted in some way.

Without us seeing the offending worksheet, it's hard to know exactly what to advise as I can duplicate the problem.

Hope this helps...