You are in Lotus formula entry mode. Do the following to put things normal...
XL2003 - Tools/Options/Transition Tab... uncheck the "Transition formula entry" checkbox. Actually, uncheck any of the Lotus compatibility items.
XL2007 - Click the Office button (the round circle icon in upper left corner of the Excel window, click "Excel Options", select "Advanced" from the left-hand list, scroll down to end of right-hand listing and uncheck the "Transition formula entry" checkbox. Actually, uncheck any of the Lotus compatibility items.