Excel Column labels show as numbers

[mrudnet]

I am working in Excel 2007 and suddenly the columns are showing as numbers
and not the usual letters (A, B, C...). How do I change this back? Thanks.

 

[Bob I]

office Button, Excel Options, Formulas, UNcheck "R1C1 reference style"

 

[JBeaucaire]

Click the Office Button
Click the Excel Options
Go to Formulas tab
Go to Working with Formulas section
UNCHECK the R1C1 reference style