Please open the program that configures the touch pad....and you can
configure it. For example, in Compaq notebook...Start>All
programs>Utilities>One touch>One touch configuration. Similarly, there will
this place where you can configure single click, double click etc.
Also, on most touchpads, you double click by double tapping the touchpad
quickly. You may need to install the software for your touchpad if it
isn't already on there. Do as John suggested and make sure all the
settings are correct in there. Also, see if you find anything about
"Detect Accidental Double Clicks" and disable that if possible.