DirectX11 Mouse Control - c++

Question

I have a 3d program in DirectX and I want to give the mouse control to the camera. The problem is the mouse moves right off the screen ( In windowed mode ) then the camera doesn't turn anymore. I tried to use SetCusorPos to just lock it in place after the mouse is moved. That way I could get a dx and then set the mouse back to the center of the screen. I ended up getting a endless white screen. Here is my camera/mouse movement code so far. If you need any more information just ask.
void PhysicsApp::OnMouseMove(WPARAM btnState, int x, int y)
{
// Make each pixel correspond to a quarter of a degree.
float dx = XMConvertToRadians(0.25f*static_cast<float>(x - mLastMousePos.x));
float dy = XMConvertToRadians(0.25f*static_cast<float>(y - mLastMousePos.y));
// Update angles based on input to orbit camera around box.
mTheta += -dx;
mPhi += -dy;
// Update players direction to always face forward
playerRotation.y = -mTheta;
// Restrict the angle mPhi.
mPhi = MathHelper::Clamp(mPhi, 0.1f, MathHelper::Pi-0.1f);
if( (btnState & MK_RBUTTON) != 0 )
{
// Make each pixel correspond to 0.2 unit in the scene.
float dx = 0.05f*static_cast<float>(x - mLastMousePos.x);
float dy = 0.05f*static_cast<float>(y - mLastMousePos.y);
// Update the camera radius based on input.
mRadius += dx - dy;
// Restrict the radius.
mRadius = MathHelper::Clamp(mRadius, 5.0f, 50.0f);
}
mLastMousePos.x = x;
mLastMousePos.y = y;
}