Mouse is too sensitive!

My mouse all of a sudden started acting as if I had double-clicked on windows and items when I'd actually single-clicked. I changed the settings in Control Panel/Mouse (fast to slow) and also in Tools/Folder Options/General (double-click to open an item, single-click to select), but it will still close two windows when I click on one, open every email that I'm just trying to highlight, etc. Help! Thanks!

Sadly, it's not even that old! And Dell support were such morons that they kept trying to send me drivers for my Touchpad mouse, even though it was the silly USB mouse. I feel almost moronic myself posting a question about a stupid mouse, but it's driving me mad. Thanks for the input!