You were cleaning or tapping the synaptics touchpad on your HP DM4 laptop (or other laptop), and the synaptics touchpad is now "broken" (doesn't work anymore), and there is no switch.
some manufacturers are choopsing to use the tapping and gesturing ability of the synaptics touchpad to do things which were not done before on laptops. The synaptics touchpad drivers are getting more and more complex. It used to be that gestures and tapping were ignored (those were the good old days). now they save $10-40 in hardware for a switch and led and do it all in software, and it's driving people nuts.
Your model If your model is not listed here, one of the basic concepts should work, check your manual.
if the touchpad truly is cracked, or the rubber surface is now tacky to the touch, you need to replace your touchpad using a mfr authorized repair shop in town, and it's going to cost about $200.
tap the upper left corner of the touchpad twice to turn the touchpad on and off. it's in the manual. you are not the only one who has complained about this. there may be some way of setting a control panel applet or notification area applet to disable tapping actions on your synaptics touchpad. manual
There is a touchpad on/off button on certain models, or do Fn+F9. it's in the manual. To disable tapping, go to Mouse Properties option in the control panel. manual