The lens can become bound by grit and dirt, it can be off its tracks, or it can be sitting crooked due to dropping it or rough handling. First make sure you have a fully charged known good battery
in the unit and it is turned off. Plug your Audio/Video cable into the camera
. Lay the camera down on its back on a firm smooth surface. Press on the shutter button with one hand and while holding it down turn the camera on. If the lens becomes free, immediately point the lens down toward the floor and use the zoom to zoom it out. Take a soft brush, such as an art brush, and brush around the base of the lens to make sure you have removed any sand, dirt, etc. from the crevice around the lens where it enters the camera body.
If that doesn't free the lens there are a couple of other things you can attempt, but these may damage the camera too. If the camera is going to be tossed in the trash if it doesn't work try these two steps.
1. Take the battery out of the camera. Grasp the camera by the edges of the top and bottom with the lens facing downward. Cup your other hand slightly and smack the face of the camera into the palm
of your cupped hand several times. Reinstall the battery and try the camera.
2. If step 1 didn't work, look closely at the lens seating in the camera. See if the gap around the lens is even all the way around. If it is not, take a thin tool of some sort that will fit into the gap at the narrowest point and softly pry the lens slowly toward the widest part of the gap. If the lens is off the pins, sometimes that will snap it back on. If you hear a small light snap. reinstall the battery and try the lens. If it works, point it face down and run the lens in and out several times using the zoom.
If this doesn't work, and again, ONLY if the camera is going to be trashed if you can not fix it, try prying the the lens out forcefully, but gently. This has worked as a last resort many times. Good luck.