I was trying out a shadowmap. But all my shadow is white. I think there is some problem with my homogeneous component. Can anybody help me? The rest of my code is written in xna

Here is the hlsl code I used

float4x4 xWorld;
float4x4 xView;
float4x4 xProjection;

struct VertexToPixel
{
float4 Position         : POSITION;
float4 ScreenPos        : TEXCOORD1;
float Depth : TEXCOORD2;
};    
struct PixelToFrame
{
float4 Color            : COLOR0;
};

//------- Technique: ShadowMap --------
VertexToPixel MyVertexShader(float4 inPos: POSITION0, float3 inNormal: NORMAL0)
{
VertexToPixel Output = (VertexToPixel)0;    

float4x4 preViewProjection = mul(xView, xProjection);
float4x4 preWorldViewProjection = mul(xWorld, preViewProjection);
Output.Position =mul(inPos, mul(xWorld, preViewProjection)); 
Output.Depth = Output.Position.z / Output.Position.w;    
Output.ScreenPos = Output.Position;

return Output;
}

float4 MyPixelShader(VertexToPixel PSIn) : COLOR0
{
PixelToFrame Output = (PixelToFrame)0;      

Output.Color = PSIn.ScreenPos.z/PSIn.ScreenPos.w;   

return Output.Color;
}

technique ShadowMap
{
pass Pass0
{  
    VertexShader = compile vs_2_0 MyVertexShader();
    PixelShader  = compile ps_2_0 MyPixelShader();
}
}