My rows have numbers instead of letters! how can i change them back?

Title says it all really!!

For some reason, instead of letters, my row headings have numbers. This is making reading formulas incredibly confusing.

How can I change the row headings back to letters?

TIA

Try this:

http://kb.wisc.edu/helpdesk/page.php?id=781

Thx USEXL

Much appreciated