Won't render the triangle if....

[abdul]

Currently, I have using the following array of vertices to draw a triangle:

        CUSTOMVERTEX g_vertices[] = 
        {
            { -1.0f, -1.0f, 0.0f, D3DCOLOR_XRGB(255,0,255), }, // x, y, z, color
            { 1.0f, -1.0f, 0.0f,  D3DCOLOR_XRGB(0,255,0), },
            {  0.0f, 1.0f, 0.0f, D3DCOLOR_XRGB(0,0,255),}, 

and I am also transforming the world matrix every time I render (in a loop) so the above triangle is rotated on X axis using the following code:

    //set the world matrics (rotate the object on Y)
    D3DXMatrixRotationX(&mat, timeGetTime()/250.0f);
        if(FAILED(lpD3DDev->SetTransform(D3DTS_WORLD, &mat)))
        {
            ShowError("Unable to set the world matrics");
            return false;
        } 

Above code works fine but when I don't use the world transformation (I don't rotate any object means I don't use 2nd piece of code^^), the triangle won't show up. Why is it doing that?