Thanks for your reply and I have found that it was a problem with my windows OS. I have reinstalled whole OS and then I am able to see NULL device in device manager.

Looks like now I am stuck with an another problem.

When I try to run it in Debug mode I am getting an error message saying "Unhandled exception at 0x004013be in EDxL1.exe: 0xC0000005: Access violation reading location 0x00000000."

VS is pointing out to the block of
Code:
void init_graphics(void)
{
    // create the vertices using the CUSTOMVERTEX struct
    CUSTOMVERTEX vertices[] =
    {
        { 3.0f, -3.0f, 0.0f, D3DCOLOR_XRGB(0, 0, 255), },
        { 0.0f, 3.0f, 0.0f, D3DCOLOR_XRGB(0, 255, 0), },
        { -3.0f, -3.0f, 0.0f, D3DCOLOR_XRGB(255, 0, 0), },
    };

    // create a vertex buffer interface called t_buffer
   d3ddev->CreateVertexBuffer(3*sizeof(CUSTOMVERTEX),
                               0,
                               CUSTOMFVF,
                               D3DPOOL_MANAGED,
                               &v_buffer,
                               NULL);
    VOID* pVoid;    // a void pointer

    // lock v_buffer and load the vertices into it
    v_buffer->Lock(0, 0, (void**)&pVoid, 0);
    memcpy(pVoid, vertices, sizeof(vertices));
    v_buffer->Unlock();
}
Can someone please help me with this.

Thanks in advance.