Row numbers are missing including all data and columns usually until the very end of the worksheet. People often search around the view tab in vain trying to hide and split the workbook but this effects the workbook as a whole and not individual rows and columns. Always check your page layout for an easy fix first though.
3 options to go about fixing this issue
1. Unhide Rows
Select the area that contains the missing row numbers and data or select all the data (CTRL + A )
Under the Home Tab - Format -> Hide and Unhide - Unhide Rows
your data and row numbers should reappear.
2. Check the Filter
Make sure you are not accidently applying a filter to your data which may be hiding everything from your very worried eyes
under the Home Tab again , click Sort & Filter and Clear any filters you may have
If all else fails run excel in safemode to rule out third party addins or other setting messing with your data. Goto Run and type in excel /safe
also check your frozen panes if your still having trouble, that is all hope it helps as usual
4. Excel Save as with Macro's Enabled
Some rows may appear blank when opened with macro's disabled or in compatibility mode, go to excel file -> save as and choose Macro Enabled Excel Workbook .
Then close and retry the workbook again