texture(...) function always returns 0 - c++

Question

I have been trying to get shadow mapping to work for quite some time now and I am still no closer than I was a month ago. I am beginning to think it may be an issue with my GL drivers because I haven't been able to see any side effects such as "light acne."
I was told to start using a sampler2DShadow instead of a sampler2D and this is what I did. However, whenever I sample the map using texture(...) the result is always 0. Why would this be happening?
I have tried entering manual depthCoord values and I still get 0. Could this be a result of the shadowMap itself (i.e the way it has been setup?) or is it a driver issue?
Framebuffer Setup
FramebufferName = 0;
glGenFramebuffers(1, &FramebufferName);
glBindFramebuffer(GL_FRAMEBUFFER, FramebufferName);
glGenTextures(1, &depthTexture);
glBindTexture(GL_TEXTURE_2D, depthTexture);
glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST );
glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST );
glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE );
glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE );
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_COMPARE_FUNC, GL_LEQUAL);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_COMPARE_MODE, GL_COMPARE_REF_TO_TEXTURE);
glTexImage2D(GL_TEXTURE_2D, 0,GL_DEPTH_COMPONENT, 512, 512, 0, GL_DEPTH_COMPONENT, GL_FLOAT, 0);
glFramebufferTexture(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, depthTexture, 0);
glDrawBuffer(GL_NONE);
glReadBuffer(GL_NONE);
glBindFramebuffer(GL_FRAMEBUFFER, 0);
Fragment Shader
uniform sampler2DShadow shadowMap;
in vec4 depthCoord;
void main(){
//The final color after lighting is stored as 'FinalColor'
float visibility = 1.0;
if (texture(shadowMap, depthCoord.xyz) == 0.0){
visibility = 0.1;
}
color = vec4(finalColor.rgb * visibility, 1.0);
}
Rendering Code
glm::vec3 lightInvDir = glm::vec3(0,-10,-10);
glm::mat4 depthProjectionMatrix = glm::ortho<float>(-10,10,-10,10,-10,20);
glm::mat4 depthViewMatrix = glm::lookAt(lightInvDir, glm::vec3(0,0,0), glm::vec3(0,1,0));
glm::mat4 depthModelMatrix = glm::mat4(1.0);
glm::mat4 depthMVP = depthProjectionMatrix * depthViewMatrix * depthModelMatrix;
glm::mat4 biasMatrix(
0.5, 0.0, 0.0, 0.0,
0.0, 0.5, 0.0, 0.0,
0.0, 0.0, 0.5, 0.0,
0.5, 0.5, 0.5, 1.0
);
glm::mat4 depthBiasMVP = biasMatrix*depthMVP;
/* Shadow */
subShader->useShader();
glViewport(0,0,512,512);
glUniformMatrix4fv(glGetUniformLocation(subShader->getShader(),"depthMVP"), 1, GL_FALSE, &depthMVP[0][0]);
glBindFramebuffer(GL_FRAMEBUFFER, Shadows::framebuffer());
renderBuffer(objBuffer);
glBindFramebuffer(GL_FRAMEBUFFER, 0);
/* Clear */
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
/* Shader */
objShader->useShader();
glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_2D, Shadows::shadowmap());
glUniform1f(glGetUniformLocation(objShader->getShader(),"shadowMap"),0);
/* Render Scene */
glUniformMatrix4fv(glGetUniformLocation(objShader->getShader(),"depthBiasMVP"), 1, GL_FALSE, &depthBiasMVP[0][0]);
glViewport(0,0,640,480);
glUniform1f(glGetUniformLocation(objShader->getShader(),"renderingPass"),1.0);
renderBuffer(objBuffer);
The majority of this code has been learned from sites such as (http://www.opengl-tutorial.org/) with modifications based on (http://www.fabiensanglard.net/shadowmapping/index.php) and the red book.