This article describes how to troubleshoot no touch with an optical monitor

A USB cable is required for touch if the optical touchmonitor is being used with an external computer

Keep the cameras and light diffuser clean:
A translucent purple light diffuser separates the black plastic bezel from the front glass.  Keep the light diffuser reasonably clean.  There is a tiny (1 mm) black dot in each corner; these are the cameras (see attachment).  Make sure the cameras are not obstructed by dust or debris.

Optical touch technology was discontinued in 2014.