Your 3D camera probably simply has rubbisch position values. Either very small or infinitely large. Check the numeric values and then open up an alternate view to check.
change the view to something else: side, top, custom
right click on the light layer and try view->look at selected layer.... there it is!
you probably would see it if you set your magnification to something very low like this:
though in custom view it is better to move the custom camera and not the magnification by selecting the track z camera tool and going back
Make sure you have not hidden layer controls under the view menu. If that does not solve the problem then check the view options. It's very easy to turn off light wireframes. You'll find it in the menu that pops up under the three little lines that make up the menu icon at the top of the composition panel.
If that doesn't help press the UK twice with all your layer selected then reset the camera position and reset the light position and any 3-D layers you have in the scene.