row numbers disappearwhen a cell in that row is selected - formula bar shows only top of d

my excel workbook has been working fine but now it has a problem: When i select data in any cell that row's row number disappears - also the formula bar only shows top half of data (unreadable). Also, if i enter text in a row it does not appear at all. I've checked several other workbooks and the same problem exists.

I've attached the workbook.

Any help greatly appreciated.