3D layers won't show when rendering. Please Help!

First, make sure you are setting up and previewing your composition using the Active Camera view.

Second, if you have a compatible NVIDIA GPU and have installed the CUDA drivers the project will have to be rendered using the Render Cue and output module using a frame based rendering engine. The AME will not use GPU rendering for Ray-traced rendering.

Third, Ray-traced rendering is deprecated, no longer being updated, never worked reliably across multiple systems and is generally a pain in the neck. The best option for creating 3D text layers is to use the C4D Lite system and the Cineware plug-in. Just set up a standard text animation using a Camera and 3D layers for text in a standard Classic 3D comp, export the camera and text move to C4D using the File>Export menu, then import the C4d file and drop it into your timeline. The Cineware plug-in will show up in the Effects Control Panel and you can open up C4 Lite will open up and you can adjust the extrusion, add textures, and do a lot better job with very little effort and it will render much faster.

If you don't what to go through the trouble of learning how to use C4D lite you can just change your rendering option in the comp to C4D Rendering. You'll have nearly all the options, the AME will not fail and things should work out much better. As with the Ray-traced renderer, you will lose some compositing and effects options but in most cases, you are much better off using the C4D renderer than Ray-traced rendering.

If none of those solutions work we need to see a screenshot of your comp with the modified properties of the problem layer revealed, see your composition settings and know a lot more about your workflow than you have provided.