glEnable(GL_DEPTH_TEST) - nothing rendered

Question

In OpenGL, I display a simple model. When I enable the depth buffer,

glEnable(GL_CULL_FACE);
glEnable(GL_DEPTH_TEST);
glDepthMask(GL_TRUE);

Answer 1

Did you make sure you clear the depth buffer?

glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
                              ^^^^^^^^^^^^^^^^^^^