OpenGL: moving vertex shader calculations to the fragment shader results in a black screen

Question

I am trying to move my vertex shader to the fragment shader to create a Phong shader but what ever I try results in a blank screen. It seems like I may be doing something wrong in the fragment shader but to me it looks fine.

Vertex shader:

attribute vec4 vPosition;
attribute vec4 vNormal;
attribute vec2 vTexCoord;

varying vec2 texCoord;
varying vec3 fN;
varying vec3 fV;
varying vec3 fL;

uniform mat4 ModelView;
uniform mat4 Projection;
uniform vec4 LightPosition;
uniform float Shininess;

void main()
{
    vec4 vpos = vPosition;


    fN = (ModelView * vNormal).xyz;
    fV = -(ModelView * vPosition).xyz;
    fL = LightPosition.xyz - (ModelView * vPosition).xyz;

    gl_Position = Projection * ModelView * vpos;
    texCoord = vTexCoord;
}

Fragment shader:

varying vec3 fN;
varying vec3 fV;
varying vec3 fL;
varying vec2 texCoord;

uniform float texScale;
uniform vec4 AmbientProduct, DiffuseProduct, SpecularProduct;
uniform float Shininess;
uniform sampler2D texture;

void main()
{

    vec3 N = normalize(fN);
    vec3 V = normalize(fV);
    vec3 L = normalize(fL);

    vec3 H = normalize(L+V);
    vec4 ambient = AmbientProduct;

    float Kd = max(dot(L,N),0.0);
    vec4 diffuse = Kd * DiffuseProduct;

    float Ks = pow(max(dot(N,H),0.0),Shininess);
    vec4 specular = Ks * SpecularProduct;

    if(dot(L,N) < 0.0) {
        specular=vec4(0.0,0.0,0.0,1.0);
    }

    gl_FragColor = (ambient + diffuse + specular);
    gl_FragColor.a = 1.0;
}