XP O.S., Microsoft Intellimouse. Said mouse has started acting up in the past few days. Whenever left clicking on anything I have to click 2 or 3 or more times before whatever I click on opens.

When double clicking is required it generally takes 5 or 6 clicks.
The device manager says it's working ok, and all the settings are correct, and the USB cable has been checked.
Right click and the scroll wheel work ok.
BTW, the problem exists when using Firefox, I.E., and all programs, files, etc. on the computer.