If you have the touchpad icon in your system tray (lower right of the toolbar) and the left button is green. Your left button is stuck. Try clicking it and see if it will unstick. (you may break it, but you can try gently prying the button, but not enough to pop it off). If you attach a 2nd mouse and go to the settings for the Synaptics Touchpad, you can enable this in the toolbar if it isn't there.
The double touch for primary click fails in this scenario because the primary click button is always pressed, thus disabling your ability to double touch. This will also happen if the right button is configured to be the primary click if the right button is stuck.