If the Marquee tool has worked correctly in the past, I would suggest a Reset of this tool.
Select the Marquee Tool, then go to the top where the Options are for it.
The leftmost icon is there is the Marquee tool. Right-click on it to show the Reset menu and choose "Reset Tool".
It should set the Marquee tool back to its' defaults.
I got a blank reply. Could you let me know if my answer worked? Click the "correct" button if it did or post a followup if it did not.
Thank you Gener7, it worked like a charm!